I know this might not be what you're looking for but I have seen some guys on youtube videos get a pair of underwear (Hopefully not a 50 dollar pair!) and they will cut the "brief"

part of the underwear and leave only the elastic. Then they will cut a slit through the elastic in the front and slide the packer there and depending on the size, it will hold the packer in place! Also I saw another video where it could help to do what he did. I'll give it to you in a sec!
Here's video!
FTM Colden: How I packYou could always just buy a harness for the packer too

Best of luck
Here's another video. I like this guys vid's. Haven't seen this one but I trust it will be of some help. There are plenty of videos out there with this subject. Hope I helped
Cheap Easy Packer Harness