Lowering my FG with more sugar/honey

[bosunbrew]

I brewed a 5 gallon batch of Centennial Blonde over a month ago. Hit my OG at 1.039, but my FG stalled out at 1.018, which is way too high. Target FG is 1.008.
I use the Brew in a Bag technique, and tested w/ iodophor for conversion. Mashed at proper temps for 90 minutes. For some reason, I'm just not getting enough sugars. I pitched 2 packs of hydrated Nottingham dry yeast.
So, I messed up an easy brew. I'm wondering if I can bring the final gravity down a bit now, by adding either corn sugar or honey? I would definitely boil the added sugar.
I'm not worried about the flavor changing or the beer falling out of any category, I just want something that won't be so sweet... so I'm hoping to restart the fermentation by adding the adjunct sugars.
Has anyone had any luck with this or even tried this? I'm wondering how much sugar/honey I need to add to drop my FG down to around 1.010.
For some reason I'm having terrible luck lately in getting my FG to drop. I need to do some more research to make sure I'm getting all the sugars out of my grains during the mash. Maybe I need to mill my grains down so they're a bit finer. Any ideas for saving this brew?

 

[Nateo]

If the problem is lack of fermentable sugar, then adding simple sugar will solve the problem. I would guess the problem is yeast or fermentation related. Are you doing forced ferment tests on your beer? That's the only way to know if your FG issues are mash-related or yeast-related.
http://braukaiser.com/wiki/index.php/Fast_Ferment_Test

If it's yeast related, I would try rousing (swirling to get yeast back into suspension), then I would try racking onto another beer's yeast cake, or adding a very active yeast starter.

If it were a grind/mill issue, you would miss your OG, not your FG.

 

[jaycount]

What temps did you mash at?

 

[flananuts]

What was your grain bill and what temp did you mash at? You could have a higher percentage of unfermentable sugars as well.

 

[bosunbrew]

The grain bill was:
7 lb Pale Malt (2 row)
.75 lb Cara-Pils
.50 lb Caramel/Crystal
.50 lb Vienna Malt

I mashed at 150 degrees for 90 minutes.

Nateo- thanks for that link. I had never heard of the fast ferment test. I will have to read up on it. I think I might add an active yeast starter, along with possibly adding some sugar. At the worst, I'm going to carb some sweet beer. Maybe I'll dry hop it, if it tastes too sweet. Time to have some friends over and help me kick a keg. Well, I learn something with every batch.