I would keep in mind that this is not a great ion to be drawing resonance structures for. Any other resonance structures that you draw will be making a very minor contribution to the structure. You could do what Hunter is suggesting, or you could also break the CN pi bond onto the N, creating two positive carbons.
Neither structure seems to suggest any stabilizing effect. In fact, the carbocation is quite destabilized by having the cyano group next to it, mainly because of the inductive effect I believe. Both resonance structures you end up drawing make a much smaller contribution to the structure than the originally draw one. Incomplete octet on nitrogen is terrible, two positive charges on carbon is terrible.
There doesn't seem to be much point to drawing these resonance structures without offering some kind of caveats like this.