I guess the only thing you could do is rename the dcc windows when one is initiated, putting an index in the name of the window, using a character in between the nick and the number that can't be part of a nick. You can use $window(=<nick><char>*,0) to distinguish between how many there are already with that nickname that you indexed to find the right number to add.
I know it's (very) crappy, but that's all I can think of. Besides coding a DLL perhaps.
I guess we could start by making it a feature suggestion, who knows, it might even be implemented in the next version.
EDIT: How's the RSS thing working out?
