Dang, it only finished at 1.029? Yikes...that beer will be ridiculously sweet. My guess is you way under aerated. A 4L starter should've been plenty, at least to not under attenuate to that degree.
Yeah, I'd maybe try what ajk suggested. Pitch a pack of 34/70 into the keg, rig a blow off with a piece of hose attached to a gray gas disconnect, run it into a jar of sanitizer and let it go at 65 for a bit. You're not gonna want to drink that beer.
Last resort, you could get some Amylase Enzyme, pitch a teaspoon of that, let it go for a week or 2, then rack to a new keg.