Dunno if you've made any progress, but as far as I know, if you don't want to buy an extra memory card (something I may concede to myself soon), you'll have to use the backup/account switching techniques for the one card. However, beware as the "sub" account doesn't store trophies properly.Oh, I know it's a cross buy. I just don't want to go get a new memory card just so I can play Guacamelee on my Vita.
Basically, I use both a UK and JP account on my PS3, but any demos and such downloaded from my JP account won't transfer to the Vita (which has my UK account registered to the card).
Oh, and I guess I should say I'm getting this game asap! Looks like a lot of fun, and a great addition to the Vita's slowly growing library. Cross-buy makes it a definite purchase.