You can trigger a sample for free, using Regate and Resamplamatic 5000. The gate will actually allow you to mix between the triggered sound and the mic'd sound. I usually set my threshold so that it allows the drummer to be dynamic, but when they are playing a solid beat, the trigger comes into play (but not abruptly). You can add a comp after the gate to turn down his mic'd kick if you have to when he reaches the sample threshold.
I also like to use a sample of the actual kick drum that the drummer is using so it has some realism to it. I edit the sample in my home studio to get the ideal sound that I'm after, sometimes adding a low sine wave to it or whatever I need to do to get the sound I want. You can get away with doing it live too, if you have an empty room to putz around with it.
The only thing that you really need to change in the sampler settings is the pre-delay, which is at 1ms by default, and I take off the 'obey note off' option.