Hey guys, I'm just recently getting into acoustic guitars and I'm going to be purchasing a Martin 000-15m soon. Sometime in the future, I'd love to throw a pickup in it when I start to play more acoustic shows (for now I'll just throw a mic in front of it). I've heard the in-body microphones and those things sound great! BUT I would rather not have to put any holes in my guitar to mount one, do you guys know of these that don't require any mounting?
Nice guitar. You could use a soundhole pickup (I have a Baggs M1 Active) and run it direct to the amp/PA. You can add some security by having a tab on the cable that hooks on the endpin. I've also experimented with sockets that hook on the endpin.

However, I would install an endpin jack. It won't affect the value of the guitar, it will provide greater security, and it will allow more pickup options.

I happen to like soundhole pickups, installed permanently to an endpin jack, but there are plenty of good choices. For example, the K&K Western Mini is popular, running to an external preamp like the Red-Eye
I use a Fishman Matrix Blend in my guitar. All it requires is the endpin jack and the controls mount within the soundhole with adhesive. It's a piezo under the saddle and a gooseneck condenser mic that you can blend in to the piezo signal. It's (relatively) expensive, but it sounds gorgeous and records great. I run it straight to the PA live and have been very satisfied with it.
I use a K&K pure mini. Its a three head bridge plate transducer. Great passive pickup especially for percussive guitar. It does require an endpin jack.
I don't even use a pre-amp with it. I just go straight into a PA and it sounds fine