As an interim solution, pop one of the wheels off of an extra SG+ rear end and chuck the rear end into a dremel tool. Then use the remaining wheel as a platform for sanding down the stock tires so they are perfectly flat instead of ridged up on the edges. Try to sand them all down to the same diameter or create pairs of various diameters. The stock diameter is around .455 and a decent middle of the road diameter for a box stock would be around .440 or .442. When you are done sanding and sizing them, apply a few tiny drops of super glue gel to the rim to hold them on a bit better. When you sand them keep the pressure light and don't spin them too fast so they melt or fly off the rim. Don't try to go much smaller than .440 because the stock tires are a bit thin. (I've never tested the limits. You can always freshen them up by taking off a tiny bit more with a fine emery board while on the car.) The results will be a big improvement, not as good as silicone, but something to hold you while you acquire other wheel and tire options.
[Edit]
Added picture. The pair on the top are the stock "cupped" tires. The pair on the bottom have been sanded flat to .442. As you can see it is possible to get the stock SG+ tires flat. The camera angle makes the top set look huge, but the difference is only about 12-13 thousandths.