Use an under-wing hydraulic jack situated at the wing tiedown point. Be sure that the upper end of the jack is safely secured to the tiedown bolt/ring. Do a SEARCH under "Jacking" for further ideas.
Alternatively, put some form of clamp (e.g., wood, steel, or even a hefty C-clamp) on the gear leg and lift the leg with a jack - use some form of padding so as not to scratch the paint on the gear leg.
Some have tried using a U-shaped steel bracket that slides up the gear leg and serves as a jack point, but on the RV-12 the brake line gets in the way.