Unfortunately this would require a lot of work. Because I'm on Android now there isn't a ton of incentive for me to implement something like that. I'm open to helping someone out with it.

It looks like Grooveshark has an API though (http://developers.grooveshark.com/) - That would actually be quite nice. Someone could request API access to Grooveshark and then modify pyRadio to support Pandora + Grooveshark (keeping in mind you'd have to enable the ads and grooveshark message when someone selected to play from Grooveshark. Definitely not a bad compromise.)

Slacker doesn't have something like that.. so it would require someone to either find an app that has already reverse engineered their API - or do it themselves which is insanely time-consuming.

ETA:
You could cheat, using something like this:
http://digg.com/newsbar/topnews/Linu...or_Slacker_com

Which essentially loads the 'mini' player of slacker into a little python widget window. But it would still be flash, bulky, and resource intensive .