Have it similar to the sapper in the way that it has those things that come out of it that encompass the entire sentry it saps. Like on a level three, it's wires are different then a level 2.
So you could have some type of thing that, when the flag is capped, spurts out some type of gripping mechanism, be it hooks that stretch to fit the nucleus prop, or be it suction cups that do the same.
I'm implying you use the nucleus prop, with just a different coloured spinny thing. Thus the modeller could use the nucleus prop for sizing.