I don't think getting "respectable" collaborators will be that hard, once the World War is over. Look at all the Kadets who served in Skoropadsky's cabinet in Ukraine.
https://books.google.com/books?id=yLiLYtkfJ_YC&pg=PA309 I can see the arguments the newly found friends of Germany will make: "Yes, we supported the Allies, but the war is over now, and the important thing is to beat those horrible Bolsheviks..." Even before the War was over, while the Kadet Central Committee rejected German overtures, "some prominent Kadets did waver in their loyalty to the Allies. None other than Pavel Miliukov, perhaps the most prominent Kadet leader, seriously explored the possibility of accepting German help to overthrow the Bolsheviks..."
https://books.google.com/books?id=8RyNOw0jfdoC&pg=PA68
Miliukov did indeed explore the possibility of an alignment with Germany, but it's important to note how their meeting actually went: Miliukov demanded the reversal of all Russian territorial losses except those in Poland, the Germans refused to consider any major revision of the Treaty of Brest-Litovsk, everyone went away dissatisfied and negotiations were broken off almost immediately. And Miliukov was still vigorously denounced and marginalized by the Kadet party and the whole White mainstream for his overtures.
(As an aside, neither Miliukov nor the Kadets as a whole were exactly the respectable liberal opposition they had once been. They had swerved sharply to the right and their visions for Russia's future swung between a strong, quasi-constitutional monarchy and a thinly veiled monarchist dictatorship. Miliukov was among those leaning towards the latter.)
For the White mainstream, "beating those horrible Bolsheviks" was only one half of the point. The other, no less important half, was to resurrect a "Russia one and undivided", or at the very least
something that in no way resembles the borders of Brest-Litovsk. They were not interested in ruling a mere fiefdom in the patchwork of
Mitteleuropa and they consistently rejected that road.
My primary source for the above:
Russian Nationalism and Ukraine; The Nationality Policy of the Volunteer Army by Anna Procyk
. Can't find readable links right now, unfortunately.
The only faction even slightly inclined to accept cooperation with Germany without fully renouncing the ideas of Brest-Litovsk were former Black Hundred leader Nikolai Markov and his fellows. A small, unstable and thoroughly unpleasant crowd.