OK, here's an idea that is not exactly "compensated emancipation" but which some Lower South senators feared would amount to something like it for the Border Slave States:
On August 20, 1850, Senator Thomas Pratt of Maryland moved an amendment to Senator Mason's proposed Fugitive Slave Act. It provided that the federal government should compensate slaveholders when Northern hostility made it impossible to return a fugitive under the Act. Pratt's amendment was defeated--about half the Northerners opposed it, the other half abstaining. Because of the abstentions, it could have passed if it had overwhelming Southern support. Pratt prayed that all Southern Senators "would upon this question (although they have upon no other) been found shoulder to shoulder." This did not happen. The Pratt Amendment got strong backing in the border slave states--these states were of course the ones with the greatest risk of losing fugitives to the North. (True, the total number of fugitives was never very large, the census indicating it as about one thousand a year. But the loss of even relatively few slaves could be a serious financial blow--at least to the Border South areas where such losses happened most frequently--given high prices for slaves.) What killed the Amendment was opposition from most of the Lower South's Senators.
Their arguments were interesting. Senator Turney of Tennesee charged that the Pratt Amendment was intended "to emancipate the slaves of the border South, and to have them paid for out of the Treasury of the United States." Turney envisaged border state residents telling their slaves to flee, whitening their region, and enriching themselves. Worse, warned Senator Andrew Butler of South Carolina, "dishonest masters" might encourage their slaves to run away to get an inflated value for them! Turney, Butler, and Jefferson Davis all thought many border state whites would welcome this "mode of emancipation." Senator Underwood of Kentucky tried to reassure his Southern colleagues that although "many" Kentuckians thought slavery a misfortune and "are anxious to get clear of it", only a "very small minority" would accept emancipation without black removal. While blacks stay, the white Kentuckian would remain "the most ultra southern man you can find on the face of the globe." Davis replied that the Pratt Amendment would result in precisely the black removal and financial compensation to slaveholders that would give Underwood his requisite conditions for deserting the South.
Suppose the Pratt Amendment had passed. (It would be difficult for many Northerners to vote for a measure compensating slaveholders, but let's at least say that more of the Northerners who voted against it in OTL would realize its antislavery potential and at a minimum abstain. Also, let's assume a few more Lower South Senators say, "True, we don't have as many slaves escaping as in the Border South, but we do lose some, and it is difficult to recapture them, so at least our slaveholders should get compensation when loss canot be avoided. Besides, it is an insult to our fellow slaveholders of the Border South to assume that they will do the sort of things Senator Butler suggests.") Two possible effects:
(1) Could the Amendment indeed have undermined slavery in Maryland, Kentucky, and Missouri (and perhaps have delivered the coup de grace to what little slavery was left in Delaware) as Turney, Butler, and Davis feared?
(2) Northern anger at, and resistance to the Fugitive Slave Act (and Southern anger at Northern resistance) was one of the factors intensifying the sectional conflict of the 1850's. William W. Freehling suggested that "Armed with the Pratt Amendment...federal officials might have dampened Northern rage, by not pursuing fleeing slaves within resisting Yankee communities. They could then have eased southern anger, by providing compensation for lost slaves." (*The Road to Disunion: Volume 1, Secessionists at Bay 1776-1854* [New York: Oxford University Press 1990], pp. 504-5)
https://books.google.com/books?id=iqdoAgAAQBAJ&pg=PA504