I drill a hole in a piece of smaller rock/rubble, and then glue it into that. Then I place that rock in the tank and I start it lower in the tank and slowly raise it up to it's permanent location. You can then glue/epoxy the smaller rock where you want it.
I took take it off the plug if possible. I too hate plugs. There are couple pieces that are not worth taking of the plug (hawkins, phils, soli) are a few that come to mind. I have found deep holes where the plug goes all the way in. EVERYONE complains about these plugs and ORA doesn't listen. If you want proprietary plugs fine, but at least make them out of something we can cut.
I squeeze the plug with plies or vise grips. They pop right off. I can't stand the black plugs.