I thought I'd illustrate how I prop up my front end, to unload the springs, check wheel and steering head bearings, take the front wheel off, measure sag...
With the bike already on the centerstand, use a block of wood about 13.5* inches in length, and lean it up against one of the case-half bolts.
(http://img103.imageshack.us/img103/3021/bike0056bo.jpg)
(http://img514.imageshack.us/img514/1862/bike0047uo.jpg)
Then, when you push down on the grabhandle the block of wood will rock under the bolt
(http://img514.imageshack.us/img514/696/bike0077nd.jpg)
And, volia!
(http://img118.imageshack.us/img118/3698/bike0066ic.jpg)
* It has been brought to my attention that fork position in the triple clamps may affect that number!
If the forks are at the stock height (caps flush with the top of the top triple, not including the rubber plug), then yes, a longer board may be needed.
My forks have, indeed, been raised through the triples, so I only need the 13.5 inches to gain clearance.
Thank you for bringing that to my attention, beRto!