Adding Sugars in two stages to the primary fermenter when brewing high gravity beers.?

After several atempts at a high gravity Russian Imperial Stout without what I would call sucsess .( my fermentation stops after about a week. I used 2 vials of White Labs liquid Irish Ale yeast. Fermentation started within 24 hours and krausened to a large head within 36 hours then slowed down within 7 days I racked into my secondary and fermentation never resumed I re Inoculated with 2 Wyeast Acctivator packs still nothing and Its been 48 hours in the secondary. my starting gravity was 1.100 .The guy at my local brew supply is a huge fan of high gravity beers and he told me he holds back adding all the sugars to his wort and actuly ferments the first part as a starter then adds the rest of the sugars in a second wort after the yeast is at full kraussen to the primary fermenter . Has anyone ever heard of this .It sounds genius ,Using the first part as your starter.Also Is there anyway to restart what I already have or should I just go ahead and keg it