Which antennas (if any) are you using?
Have you considered a "Dummy Load" (if this is for testing)? A dummy load being basically a high-wattage resistor to absorb the transmitter's output without radiating (much).
If you needed to greatly reduce the power, but still emit *something*, consider putting a length of coax between the AP and whatever antenna you use. There's enough attenuation in most common coax, you wouldn't need much ... and you can do a rule-of-thumb ballpark based on the transmission characteristics of the coax you select.
That's about all I can come up with ....
Good Luck
Scott
