hello.
Currently
currently you can hold down the L2 or R2 and while doing that press the opposite corresponding key, R2 or L2. and this brings up half of a XHB corresponding to the order in which the buttons were pressed.
you must hold both L2+R2 at all times to keep the additional XHB up.
Suggestion
using Toggle or Mixed mode to keep up the additional XHB even after releasing one or both of the buttons. if we can release both buttons then the next time you press L2 or R2 it just brings up that portion of the XHB of your last used XHB. or by default could be Set 1.