I'll agree that uncarbonated beer definitely has a thin feel to it, especially if it's at fermentation temps.
I added a half pound of dextrin malt to my last brew (5 gallon batch) and I think it made a significant improvement to the mouthfeel. Probably too late for this batch, but maybe for the next one...
Primary: North of the Border Vienna
Secondary: West Coast Blaster
Kegs: Common Room ESB, Belgian Wit
Bottles: Steinbart's Oatmeal Stout