This is a preview of a blog post comming up in about a week.
Top Ten ways to restart a fermentation
1) Give the fermenter a swirl.
Try the easy things first. You might be able to squeeze a few more points out of the fermentation by gently coaxing the yeast back into suspension.
2) Move the fermenter to a warmer area.
Fermentation temperature can change attenuation by about 2%. That might be enough to get over the line from cloyings to malty.
3) Repitch with a higher attenuating yeast
Champagne yeasts will ferment simple sugars to completely dry. Try adding a packet of EC-1118. At this point in the fermentation the flavors have already been added by the beer yeast, so adding this second yeast will not impact the flavor much.
4) Add simple syrup.
Sometimes the yeast needs a little kick in the pants to get going. If you are adding yeast, then it's easy to add a little extra sugar to make sure the yeast starts up.
5) Add yeast nutrients.
Especially if the beer was under pitched the yeast can run out of nutrients. It takes special proteins for yeast to convert long sugar chains found in malt extract and worts generated from high mash temperatures. The yeast nutrients will give the yeast the proteins that they have depleted.
6) Add beano
Beano will break the longer sugar chains into shorter ones. So if the yeast in the fermenter cannot digest the long chains this will help them continue their job of conversion.
Other ways to fix the high final gravity without restarting fermentation
7) Dilute the beer
A final gravity of 1.020 will taste pretty sweet, but if diluted to 1.015 it might not bee so bad. The hop bitterness and the flavor will also be diluted, making it a different beer, but this may make it drinkable.
8) Add hops
A little bit of bitter will balance out the maltyness. You could add a couple of ounces of hops right into the fermenter to dry hop the beer, or make a hop tea. Either boil the hops in a approximately a 1.020 wort for 30-60 minutes to get some bitterness, or steep them for about 10 minutes in water to just get the earthy flavor.
9) Add fruit
If it's already sweet, then run with it. Fruit, by itself, is sour in beer because most of the simple sugars that they contain are fermented into alcohol, so having some malty sweetness will make a beer that the lady folk will love.
10) bottle it.
If all else fails, or you decide to leave it for other reasons, change the style name. Maybe the recipe was for a Porter but now you have a Dunkel. Maybe your American Lager is a Bohemian Pilsener.