firstly you need pkg´s. i tryed it with ps3 pkg´s but the vita gave me an error everytime i try to install something.
to do this, you need to put the vita pkg´s to hdd0>vsh>game_pkg>(a dir. with random numbers and letters, the vita pkg´s have to be stored here
i will try later to download something and to install, i am in university right now and can´t test it yet.
i installed the xmb mod v1.5. after that there are some pkg´s stored in the right directory, like xmb mod language pkg´s, but i can´t install them.
and yes the psn bubbles are visible under cma if you downloaded them to ps3