There's no reason you couldn't code your own "getmouse" routine

SUB getmouse (x%,y%[,[b%][,[wheel%]]])
b%=0
wheel%=0
DO
if _MOUSEBUTTON(1) THEN b% = b% OR 1
if _MOUSEBUTTON(2) THEN b% = b% OR 2
if _MOUSEBUTTON(3) THEN b% = b% OR 4
wheel%=wheel%+_MOUSEWHEEL
LOOP UNTIL _MOUSEINPUT=0
x%=_MOUSEX
y%=_MOUSEY
END SUB

Notes:
1. I'll be implementing custom SUB formats soon enough, but they aren't available yet!
2. _MOUSEWHEEL is not implemented yet and may differ from the usage shown.