I've experimented with HDR photography a bit and you can't do a perfect HDR merge in After Effects using only plugins or transfer modes. 
But if your source footage has a very wide latitude, then you can use simple layer stacks to recover shadows and highlights.  In 32bit mode, stack your 3 layers on top of each other with the add transfer mode, and then use an adjustment layer on top of them all to control exposure and recover highlights. 
I've played around with combinations of 'exposure', ' HDR highlight compression', 'HDR compander' and 'levels'.  Depending on your footage you might get a better result than a straight 8-bit pass, but render times are very slow.