Well don't know what program/method you are planning to use but with Toast anyway it is a simple matter of duplicating the Toast program and then running both copies. Each can then be dedicated to burning to each drive. Not all programs will allow this but Toast has had that functionality since at least Toast 8 and I will assume earlier as well.
If you are just planning to burn from the finder, there is no issue with that either. Just stick in two blanks and they will show up as burn folders on the desktop.