If you can get access to a half decent condenser microphone you should be able to EQ the room too.

Set up the microphone in the listening position (where you would sit) and then send a pink noise signal through the monitors.

Record what the microphone hears onto an audio track in your sequencer (don't monitor the track whilst recording unless you want horrendous feedback).

Analyse what the microphone picked up in a spectrograph and you will then be able to see if there are any major dips or peaks in the frequency range. If there are you can adjust (depending on your setup) the EQ on your monitors or better still, a graphic EQ that sits between your soundcard and monitors to try to achieve a flat EQ response. Note, if there are massive dips its probably because your speakers are out of phase.

This method is not as effective as attenuating the room modes but its quite a useful, easy thing to do.