Holes can be hidden in a number of ways. They could be concealed in a black background (in flutes covered by a shroud), or just on a black background, or carefully concealed in a grenade section, which would let come sound out. Acerocket's Obi-TPM comes to mind, I believe that's how he did his. The holes could be a design element of a saber (which I am doing in an upcoming saber).
It can be done, you just have to be creative. ;)