It is possible to route the exhaust (and thus the smoke) out the wingtips. You need a relatively large model and large engine to do this. (and lots of building skill...)

An easier way is to use "smoke flares" mounted at the wingtips and ignited by servo operation, similar to a remote system to set off a model rocket. Again, adequate knowledge of the equipment and how to set it up will require a fair amount of experience.

About the best 2nd plane on the market is the Sig Four Star 40. Definitely not large enough for the wingtip smoke systems...