Yes, for the horizontal overscan this can be easily done by using the "Preset Width" option in the "Display Settings" menu. You have to go to display settings and select a preset width that is large enough. Choose something wider than 320 to display the overscan. For example choose “Display and Sound” and then “Preset Width 352” or maybe even “Preset Width: 384” for the full horizontal overscan display. Just cycle through the all the different menu choices for Preset Width to find one that works for the game you are playing.
This is needed also for The Settlers to see the full border, for Pinball Illusions to see the ball on the right side of the screen, etc.
After you do that, you can still change the vertical overscan height and center the image vertically. This can be done either via the quick shortcuts “Plus+R+dpad” in the game itself, or you could use the "Displayed Lines" and "Vertical Position" options in the menu.
But the horizontal width adjustment can ONLY be made in the menu, using "Preset Width." There's no quick shortcut for that.
This is one of the benefits of this emulator: I have been working on improving this emulator for over a year with Cpasjuste’s, Schlauchi’s, and the users’ help with bug reports on the Vita already. Of course it is not perfect, but a lot of things have been fixed over time already.