I doubt it's that easy. I'd think that drug residue added after the fact to a blood stain on gauze is very different in appearance from the real thing.
I’m not certain it would be simple either.
HGH might still be detectable in the blood stains (not sure if it “stays” over time). Remember, HGH occurs naturally in everyone’s system. (Is there an age where we cease manufacturing it?)
If some is added at a different time, that might be easy to prove by similar oxydation levels or impossibly high concentrations relative to the amount of blood.