Paper gasket, on bottom of ATV aluminum block engine, drips oil in one small spot. Can this leak be stopped by external means?
Generally, No
You could try some RTV after cleaning the outside of the area extremely well and letting it sit overnight before riding it again. But don’t be surprised when the leak returns.
If you can find the torque specs you can loosen all the bolts say 1/4 turn and re-torquing them in the proper sequence.
A problem with applying something like RTV to the outside is that the pressure from the inside will tend to push the plug out, and the bubble behind the patch will fill with oil. That oil will eventually work its way out. You could keep patching with RTV, but your best bet is to replace the gasket.
If you are out in the woods and no way to buy a gasket, you might could try making one out of a cardboard cereal box. Trace it out, cut it with scissors. Might work.