Looking thru latest CW and in Service section was a new tool by Motion Pro.  They have made a screwdriver/punch type device to use for adjusting shock-spring preload especially on dirtbikes when access prohibits a spanner.  Appears to do good for the shocks with a adjuster ring and a jam ring combo.  It's made with a tip that shouldn't mess up the stem ring slots and a heavy end for driving.  Motion Pro Shock Spanner Punch #08-0483 and maybe about $19.00.   Just a possibility???

Roger

Hey good find.  That looks like it just might do the trick and save a few dollars

IIRC McMaster-Carr has the proper tool for less $. I'm sure the collective will chime in here...I always use a Ford wrench and screwdriver.