Adding maltiness to a finished brew

General Homebrew Discussion
1

I have an Oktoberfest that came out a little thin.  Nice and clean, but without the malty character that I expect in a Marzen.  Maybe my mash temp was a little low.

Is there any way to adjust the already-kegged brew to add some maltiness?  I have a week between now and when this beer is going to be served.  Unfortunately I don’t have another, stronger beer to blend in.

TIA.

2

Would it be possible to go to the store and get a bottle of Optimator or similar Dopplebock? One per five gallons might do the trick.