First, OP understands that the stab jacks aren't levelers, so use your reading skills folks.
OP, to me, it seems the level of effort required to level with jacks or under the wheels is of a similar effort, however your idea is pretty creative and sound IMO if you want to go through that effort of installing.
The one down-side I see is stability or frame flex potentially. Currently, trailer is supported in basically 5 spots per side, tongue jack, front stab, 2 axles and rear stab.
You'd be reducing those 5 points to 3 effectively. I'd do a test manually. 1/4 and 3/4 points on the frame seem about right. I'd just crib up at those points on one side, taking weight off the wheels and see how it feels from a flex standpoint and verify your jacking points will be acceptable before diving in with a permanent solution.
