Add these lines to your .Xdefaults:

 Xcursor.size:         22
 Xcursor.theme:        Grounation
!Xcursor.theme:        Grounation-left
!Xcursor.theme:        handhelds
!Xcursor.theme:        jimmac
!Xcursor.theme:        pCircle-24
!Xcursor.theme:        pCircle-32
!Xcursor.theme:        pDebian-24
!Xcursor.theme:        pDebian-32
!Xcursor.theme:        pSlackware-24
!Xcursor.theme:        pSlackware-32
!Xcursor.theme:        pSuse-24
!Xcursor.theme:        pSuse-32
!Xcursor.theme:        pTux-24
!Xcursor.theme:        pTux-32
!Xcursor.theme:        pUbuntu-24
!Xcursor.theme:        pUbuntu-32
!Xcursor.theme:        redglass
!Xcursor.theme:        whiteglass


And use the ! for a commentsign. So the line without an ! in front
of it will be used.