Low profile or slim basking lamps??

[Maleficentsdragons]

I'm setting up a new stack for my hatchlings but have run into a problem. My t5's Take up the whole width of the indent and I can figure out how to put a heat source.
Would sticking a heat mat to the side of the vivs, or shining a heat lamp from the outside work? Or do they make super slim heat sources I don't know about?
Top of these are plastic, sides are glass. I've only got about 11" of total depth to work with. 7" with the drop down.
...I've attached pictures. Thanks for any advice!

 

[Taterbug]

That's pretty short, I'm assuming due to space you need them stacked? Dragons really do best with overhead radiant heat. Heat mats are really bad at that and I'd think a light outside would mostly heat up the glass.

You could get away with heat panels (on thermostat) they are very thin, but that won't be a very economical way to heat.