Crazy idea: How much head space do you have? 5 gallons of beer in a 6 gallon carboy? If so you have about 1/2 gallon of wiggle room that you could use. Bring 3/4 gallon water to mash temp...mash in 3/4lb of 2 row and the 3/4 lb of munich. You would get a gravity around 1.055 (depending on efficiency) and your grain absorption would be around 1/4 gallon.
^Note, I've never tried this..but in theory..!