I see this too many times, the fun thing is when the Orks turn out to be running all Battle Wagons and the Combi-Melta would've been really helpful.
If it's not clear on the list make them role randomly for it
How about sticking to what the model really has?
Magnets should do the trick
Where i play, unfornulty all people playing marines or IG (or tau battle suits) do that, the special weapons are "fixed" by magnets
It's a pain then their list has "combi-weapon +10PTs", i faced someone that made all combi-weapons as combi-plasma (i play marines most of the time)
Btw, he still lost, i went with a troll army (2 landraiders, 1 predator destructor, 2 tactical, 1 librarian) the combi-plasma were useless (i asked nicely, before the game started, what were his special weapons, and he replied, "......vs marines they are combi-plasma")
Three words "Rare Earth Magnets"
I've been tempted to do this with power weapons. After all, it simply points to how they are modeled, and they all listed the same on the army list.
Dark Space Elves
Titans & Knights
Ye Olde WMS