Bit of an oversight on the devloper's behalf. (And by that I mean HUGE OVERSIGHT when you go ahead an offer free Vita versions with the PS3 copy) If you have (and use) an alt PSN account on your PS3 that isn't also on your Vita you can play a regular online match and just watch the screen. Of course most of us used our primary PSN account on both our PS3 and our Vita and you can NOT invite youself to a match.
Sony had recently added "cross-controller" compatibility to the Vita which works for LBP2 but sadly Superbot didn't include it in PSASBR.
So yeah.. unless they patch in a fix, in the form of a local connect, ability to ID and invite your own account on Vita, or "cross-controller," we're pretty much S.O.L.