Turning a non remote master key into a remote key?

[phathom]

So I need a second key for my car. My options are:
A) Pony up $175 for a new remote key from the dealer
B) Pay $75 for a new, non-remote key from the dealer and live with no remote
C) Pay $75 for a new, non-remote key from the dealer, order a 315mhz key blank with remote fob, remove the key blank and use the rest of it for a fob, so I have a key and a separate fob.
D) Pay $75 for a new, non-remote key from the dealer, order a 315mhz key blank with remote fob, remove the key blank, open up the dealer issued, non-remote key, and put it in the aftermarket remote key fob case.

I'm leaning towards D, but if that is not possible to do for some technical reason. I would be happy with C.

The key I'm ordering: Part# 51218236596 https://c1552172.ssl.cf0.rackcdn.com/527053_x800.jpg

The option I'm looking at for options C and D is something like this.
315MHz Remote Entry Key Fob Transmitter Uncut Blade for BMW E46 x3 x5 3 Series | eBay
Obviously the key itself won't work, even if I have it cut.

They also have flip styles, but they're too bulky imo. If they would be a better option though, I'm open to it.

It looks like GM5 has that service for $60, but from the sound of it, they unsolder the transponder and solder it onto one of those aftermarket options I linked and cut the key blank to match. I'm looking at a more DIY approach and basically taking both keys apart, removing the blank, and likely epoxying in the factory cut key with transponder into the new housing.

If I am able to do this for myself, I would be able to walk away with a legit remote key for about half price.

Thoughts on this? Anyone do this before? Is there some technical issue, like space in the donor fob or the dealer key is ridiculously hard to open without damaging the transponder? If so, I'm fine with just getting the key from the dealer, having an aftermarket fob, and having two things on my keyring instead of one.