As an example my family came to the USA from Heidelberg in the 1880's. The local town council paid for groups to leave the Germany and paid for transit. This was pretty common in the 1880's. So what you are suggesting has happened throughout history. Both in a voluntary and non voluntary situation :
Example ::: Greece Turkey in the 1920's :::::::::::::::::::
https://en.wikipedia.org/wiki/Population_exchange_between_Greece_and_Turkey..................
According to some calculations, during the autumn of 1922, around 900,000 Greeks arrived in Greece.
[2] According to
Fridtjof Nansen, before the final stage, in 1922, of the 900,000 Greek refugees a third were from
Eastern Thrace, with the other two thirds being from
Asia Minor.
[3][4]. The estimate for the Greeks living within the present day borders of Turkey in 1914 is 2.115 million a figure higher than the 1.8 million Greeks in 1910 which included Western Thrace, Macedonia and Epirus. The Ottoman figures are 625,000 in Eastern Thrace including Constantinople (260,000, 30% of the population), 550,000 Pontic Greeks, 880,000 Anatolian Greeks and 60,000 Cappadocia Greeks. Arrivals in Greece from the exchanged numbered 1,310.000: 260,000 from Eastern Thrace, 20,000 from the southern shore of the Sea of Marmara, 650,000 from Anatolia, 60,000 from Cappadocia, 280,00 Pontic Greeks, 40,000 left Constantinople (the Greeks there were not required to leave) for a total of 1,310.000
So this is just one example of many many population transfers. So you take the new German polish areas and transfer the population to Tanzania, as seen above it can be done with carrots and sticks. Lets say Germany wishes to transfer 2,000,000 Poles to Tanzania :
1. Each Polish transfer gets 10 acres (or 20 acres)
2. Taxes or confiscation of land to "incentify" the Polish to move
3. From here it comes down to how aggressive the Germans wish to be to drive people out of the area (ie : carrot or stick)