Ok so you have to own an American account to download this. Ofcourse you can only have one account active on your ps vita at a time. Which is why I am also providing this link. (http://www.el33tonline.com/past/2012/3/26/el33t_tip_how_to_switch/) Which should enable you to change accounts without formatting your PS Vita.
You have to repeat the process again to return to your original account.
Can someone post a comment to say if this still works? Would be appreciated :) (Sorry I can't test myself)
I am unsure if the exploit still works. Havn't tried it yet but will save yourself about £5 which is cool :)
And Sony first party games are £11.99 in the PSN store UK at the moment aswell :)