Vista - VirtualPC DHCP lease time for Shared NAT

Does anyone know of a way to change the default lease time that VirtualPC
gives to a Shared NAT config? It currently seems to give a dhcp lease expire
time of 17 years 5 days.

The issue I am having is that my dns server ip's have changed. I have a
bunch of diff images all based on a few master vhd's. The master .vhd image
has the old dns ip's setup in the image. So every time I create a new diff I
have to boot the image and "ipconfig /release" and "ipconfig /renew" and then
save the diff.

Any thoughts on how to change the lease time and/or a way to force a
release/renew. Or a way to change the default ip range virtualpc gives out?

Thanks, Keith