Use G1 thumbnails during migration to G2?

I'm planning a large move from G1 (3 different sites) to G2 (a unified site) with approximately 40,000 images. My server is only a 1GHz VIA P3 (fanless - very quiet) and I know it is going to take a long time for the migration to regenerate the thumbnail images as the latest ones are 10MP. Is it possible for the G1->G2 migration tool to use the existing thumbnails in the G1 sites so I can avoid the very lengthy process? I basically worried about the process timing out; it will probably take a week. Thanks.