It's totally possible. Find a mini-mash recipe or adjust one of your own. Pick up a 5gal. paint strainer bag (available at any hardware or paint store). Put the grains you want to mash in the bag, insert bag in appropriate temperature water (according to recipe). Let soak at that temp for an hour. Remove bag and let drain into pot. DO NOT squeeze the bag, as this will release unwanted tannins. This wort now becomes the "boil water" in which you add your extract. Proceed as normal.
It's as simple as that. See viewtopic.php?f=2&t=4650
for how that same method can be used to go all-grain (although I personally found it more fun to build a HLT and mash tun out of coolers).