With most front derailleurs all you have to do is adjust the high limit stop so that your front shifter can't go past the middle position. I had no problem doing just that on my Voodoo with an XT front derailleur. If you do go that route, I recommend also shortening the chain although it isn't strictly necessary.
Here's a quick and easy way to see if it will work - screw the high limit screw in until it won't allow you to shift past the middle. If the shifting seems fine and the derailleur stops where you want it to, then go ahead and put on the bashguard.