Similar to your 5 gallon and decanting, but can't you just brew 5 gallons of lower gravity lager?. Send that over to a carboy for lagering and use the yeast cake for your dopplebock? I'd hate to see you decant off 5 gallons of scrapped beer, when you could get drinkable product with a little aging.
Primary #1:Dunkel #2:Empty
Secondary #1: Peach Rhubarb Wine #2: Empty #3: Empty #4: Sparkling Elderflower Wine
Kegged: Piker Liker Porter, Umlaut my Kölsch V
Bottles: Big 50 Barleywine, Framboise Lambic, Red Rye IPA, Dark Belgian Strong, Belgian Golden Strong, Kicked by a Moose Scotch Ale, Apfelwein, Russian Imperial Stout, Carmelite Tripel, Rhubarb Wine, Barolo Wine
On Deck: Irish Red, Surly Bender clone, Spruced Warmer, CDA