Yes, you should still aerate. If you don't aerate, you will not get any new yeast, and the old yeast may not be up to completing fermentation.
..... That is one of the problems with 'Over-pitching' is that you don't get many new yeast cells and the beer can stall before finishing. You will also get less flavor esters, and possibly more fusel alcohols.
As noted by others, just take a part of the cake and ferment normally. My rule-of-thumb, is to use about 1/4 th of the cake for a similar gravity beer.