Seems developer qwikrazor has made a new pboot that works on any firmware, note in order to use on 3.61+ you either need a second device or to do this on a lower firmware using HENkaku or even the EML writer exploit. Instructions located in the spoiler.
Here is a modded ARK-2 to auto boot whatever game or homebrew you have configured.
Copy PBOOT.PBP and SAVEPATH.TXT to base game folder,
which should be located in ms0:/PSP/GAME/ (that's ux0:pspemu/PSP/GAME/).
Then use CMA/QCMA to backup the base game to your PC,
then restore the game back to your Vita.
You should now see the base game with an ARK icon,
or to whatever icon you have changed in PBOOT.PBP,
you can also update the title for PBOOT.PBP.
For each game you want to auto boot, you will need to use a different name for the savedata folder,
so you will need to update the path in SAVEPATH.TXT to point to the savedata folder.
Included save, ARK_01234, has a file called BOOTPATH.TXT,
there you can store the path of the game that you want to auto boot.
Here is an example path for an ISO (or CSO):
or for homebrew (or PS1 game, without sound):
it doesn't matter where the game or homebrew is located,
as long as you have the correct paths, it'll launch.
To boot back in the ProShell menu,
hold L trigger + R trigger + Down + Cross, and keep R trigger held.
Do NOT use ux0: path in these files, only use ms0:.