You really don't need much to hold it in. Keep in mind that when you have limbs installed the plate is held in tension between the limb and the pocket. The sides of the pocket keep the plate centered. So, you could use the plates without attaching them at all (probably more noisy though).
I use the gray 3m double sided outdoor mounting tape to install my plates. I like to be able to remove them, and tinker around with it.
If you never want to remove them epoxy is not a bad option. You may want to see how the bow balances and you could weight the lower pocket to suit (fishing sinkers) and then set it with the epoxy that will hold the plate on.