I understand NO live rock in the QT, but can I put a piece of fake coral? I am going to be QT a Valentini puffer and I know they like to sleep perched to something.
You can put whatever you want in your QT. Most people just use large PVC fittings. However, you just need to remember 1: Don't transfer anything from the QT in the DT (aside from the fish) and 2: If you medicate, you could kill any beneficial bacteria that would have built up on the item.
I always use rock in my QT, largely for managing ammonia and if the rock gets a sickness that a fallow can't fix, then I just throw it into the woods behind my house.