OP, I just realized you wanted a concentrated wort to dilute later. How big is your mash tun? You will need a large tun in order to mash enough grains to accomplish this. It's really not recommended, but it is feasible.
If your tun is large enough, you have to get your water amounts in line. There is a limit on how little water you can use. You may have to do a single sparge to prevent having too much water, which means more grain to compensate for the loss of efficiency, and therefore a larger tun to hold the extra grain.
The best thing is to stick with PM, IMO, while looking for equipment upgrades, like larger kettles, MLT, burner, etc.