Already previously requested:
http://bsplayer.com/forum/viewtopic.php?p=40481#40481
As a workaround you could probably hide mouse pointer at (e.g.) top-right or bottom-left of the screen (and then let the mouse rest on its back?).
Did you already try to (re)define your mouse-buttons/wheel:
rightclick > Options > Preferences > Key definitions & WinLIRC?
Select function, then place pointer in either of the two boxes at north east and then press mousebutton/wheel.
If the definition is already in use, BS.Player will tell you in the south-east corner.
(Note you have to define separately for full screen and for windowed mode).