There are a number of reverse cam retro-fit kits available. I believe BimmerTech, AlekShop, etc sells them for the F30/32. It should be the same for the F80/82. They're not cheap, but you're paying for the coding so that it works smoothly with the OEM functions. It's a lot cheaper than the Exec Pack tho
There are DIY's about installing it, again on the F30 and E90 forums. It's very easy if you have some experience doing this kind of thing (pulling off trim pieces, removing the radio). You could also have a shop do it.