Easiest way would be to get some fuel line, or better still some bump stops (which will last indefinitely, where fuel line tends to dissolve quite quickly) and put them inside the shocks, on the shafts, below the pistons. You have to take the shocks apart to do the job, but it's not hard.
Here's a link for the bump stops for the BB shocks, each one will lower the ride height by about 10mm http://www.ebay.co.uk/itm/HPI-SAVAGE-FLUX-2350-RUBBER-BUMP-STOP-4PCS-/310329213726?pt=UK_ToysGames_RadioControlled_JN&hash=item484110031e
If you can find any knackered shocks from the older 8 shock savvy's, they're actually better, being longer and thinner. Maybe put up an add in the wanted section and see if anyone has some going..?
If you do this mod, you might want to take some of the spacers out at the top of the shocks, as it will shorten the travel and stiffen the ride up.
Hope that helps