With a (Eureka)Sound Hole Pickup Mount you can add a pickup to your acoustic guitar or acoustic bass quickly and easily, with no guitar modification.
This model is for sound hole sizes of 3.75", and for a circular EMG pickup.
You'll need to bring you're own cable to connect to the pickup. These
You can see another version that EurekaSound LLC offers that includes all electronics here: http://www.eurekasound.com/eshpm