I wouldn't give up on them either...
When I have a beer finish a bit low on gravity, I'll taste it to see if the mouthfeel is where I want it. If it needs more body, I'll add some malto-dextrin before I keg (or bottle) just like you would with priming sugar.
Start with a half-pound and work your way up. Use 2 qts (or less) water. That will add ~ 2 pts to your FG, but go by taste, not by the numbers.
I wouldn't go more than 10-15% of MD total.