Have you tried this
1 start lbp2 on ps3 use ps3 controller to navigate to cross controller dlc and start it it will show a message talking about cross controller
2 in vita start the cross controller thin in remote play
3 on ps3 click OK in message ps3 and vita should star talking and a file will transfer and install
4 after it install close out of remote play and star the lbp 2 cross controller app
ps3 and vita should sync and now you can use vita as controller only in the dlc story area
I didn't have any problems either with getting it all going, but I have noticed that there are times where when playing the connection just won't stay... Like every 2-3 seconds I'm getting a "no connection" message where it pauses everything until the connection is back. Granted, this only lasts a fraction of a second, but for 5 minutes straight the game pauses every 2-3 seconds or so...
From what I understand, the connection for this game is based on your local network, so it's going through your router, not the PS3 (as in Remote Play which let's you connect directly to the PS3 or through the Internet).
I wonder if a bad router connection is key here? Like, if the router isn't 100% for even a fraction of a second, LBP freaks out?