I know this seems like a stupid question but I have a client that wants raspberry filling swirled in a sheet cake, I bought the kind in a sleeve but not sure if I can mix it and don't really have time to test bake. If anyone has any ideas, I would greatly appreciate it!

Yes! I actually just looked this up yesterday. Here are a few forums with recipes I found :

http://www.wilton.com/forums/messageview.cfm?catid=8&threadid=142061

You have to read a little to get to the recipe, she says to put in the middle and swirl cause it takes to long to bake and it affects the way it rises if you put it on top!

Thank you so much, I was pretty sure it could be done.