One option would be the Full Metal Bracket assuming the plasma TV is sufficiently close to the wall. MarkSJohnson (I think) also made a very spiffy floor standing rack to hold the center speaker over an RPTV with a very skinny top, just like your plasma...

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8