Get you favorit, pleated front, kakhis - turn out the front pockets and get out your sewing kit. If nothing better presents then grap the tail of your dress shirt front but you may have sufficient cloth in the in-seam of your kakhis to clip off a strip about 1inch by 1.5 inch. Sew this to the inside back of your kakhi pockets as a little band that will hold the clip of your folder. Don't use the inside front of the pocket or it will drag down the pocket on the outside. Clip your folder to this little band and no one will ever see it. This is a simple mod that will work with any pants but hides a larger knife with pleated pants. If you want to really do-it-up you can get tailored pants with an inside change pocket sewn in that way and your will be 'stylin! or you could open out the front pocket and line it with leather or cordura sheathing similar to
these. Or if you preferr Kahki you could try
these The dockers have the fashion label and also a "hidden" cargo pocket that is accessable through the side seam that is tailored to carry a PDA without causing bulging or drooping. I'd think that it could carry a folder easier than a PDA - or as well as a PDA.