Well here's my two cents. T5's are expensive.
First thing I would do is go look at some FW Planted tank stuff. Those guys like to overdrive stuff it seems
My first experiment would be do get a 48" T8 shoplight and hook up 24" bulbs to it. See what happens - you never know
Then maybe see about getting some polished aluminum and making a decent reflector. It seems that's where T5's REALLY have their advantage. Most I've seen on here is T5's don't work well unless they each have their own decent reflector.
Heck I'm tempted to try this myself...I could use a little supplemental lighting for my 20g on the cheap.