Any options post-fermentation to "sweeten" up a beer?

you have a few options, none of which are particularly appealing. adding generic sweetness is rather easy, just add sugar or splenda in the glass. adding maltiness is a bit of a trick.

1- brew a gallon or 2 or 3 of extra light DME (or LME if you prefer) without any hops and blend. your yeast will begin a secondary fermentation but you will have significantly cut back on the bitterness.
2- do the same as above but neutralize the yeast by keeping everything cold. this is really only practical if you keg. you will likely only need one gallon of unhopped extract, but depends on the beer.

the best option by far 3- enjoy this beer as it is. it is very difficult to make a style from something that is not that style. enjoy. next time you can adjust accordingly and you are that much further along in your brewing knowledge.
Cheers.

 

No good ones. Just drink it and try again.

 

Option 1: Drink your beer and cut your losses.
Option 2: Make another batch that is maltier than you like. Blend the two batches. Weigh risk of messing up twice as much beer against possible rewards.