To do it properly, you will need to completely remove the aluminium bb shell, and inspect the interior. From there, if you can, you can attempt to sand back some carbon, and then add more carbon inside the cavity left by the aluminium shell, then sand the aluminium shell. Sand the additional carbon you just added so the surface is a little rough. Apply some epoxy resin (with the hardnerer in the correct proportion) to the inside, and allow the curing process to start (use the slower curing stuff, with 20 mins gel time). You will know this is happening when the resin+hardnener has started to warm up. (I hope your wearing gloves). Apply some more epoxy resin+hardener to the removed bb shell.
Be generous, you can always chase the thread or have a LBS do it for you. don't worry too much about epoxy dribbling inside the shell.

Insert aluminium shell. It should go in with some resistance, but not so much that it forces all of the epoxy out. Let it cure for a week before you test it, to be 100% sure.

The other option is to remove the shell, get some 2 pack epoxy you can find in a hardware store, mix it up, add a crapload to the cavity in the frame where the shell goes, and a crapload to the the shell. Jam it in there and let it set for a week.

If using holowtech cranks, you could also experiment with a combination of the 2, but also in addition reinforcing the underside of the bike's carbon shell (where serial numbers/cable guides are normally found). Remove cable guide, taking note of where it secures (make a template using the sides of the bb shell as a referance point, because you will be drilling soon). Now sand back the paint on the surrounding area's. Add 3 layers of carbon then add an aluminium plate, or preferably, stainless steel, around 3mm thick, and roughly 25x25mm. Work it to the shape of your bb shell (get creative to get the curvature). Align this so that the center of your plate is where the cable guide securing bolt is.
Now add 3-4 layers of carbon, and sand the surface to a smooth, consistent finish, ready for painting. Get your template, and taking your time, your going to drill a pilot hole, 3mm, then progress up to a size that allows your to use a 5mm tap to cut a thread. Use a chart/consult a professional for this, I would go with something that measures 4.50mm (use calipers, just cas it says 5mm, doesn't mean it's 5mm exactly). Hopefully you have drilled your hole in the correct spot using your template, and hopefully you have cut your thread correctly and you have a nice hole all the way into you aluminium bb shell, which has cured after you repaired it and allowed it to cure for a week.

Find and use a M5 allen bolt, hardened steel of the appropriate length to have a small protrusion in the bb shell (2-3 threads), use the strongest loctite you can find, and apply some torque (obviously your cable guide is back on at this point). I'd personally go with about 10nm tops. Paint. Install parts (hollowtech/ultratorque will work best, or any similar system, due to protrusion). Sorry, no Ti or normal bidon bolts allowed.

I'm definitely no expert, all my knowledge comes from working with a one of the university's on carbon stuff for the school race team, and trial and error. It's what I would do if given a carbon frame busted up like that.