You should be able to use trigger on a drum to Tap Tempo and send as MIDI Clock. The problem with trying to get the MIDI file to follow you is that you've got to play quarter-notes or some other steady pulse that the MIDI device can receive as its MIDI Clock.

Do you want the honest answer? You need to practice more and keep steady time. You don't want the MIDI file changing tempo all the time, trying to follow your poor time keeping or tempo. I'm not trying to offend you, but it is the truth. The MIDI file is going to keep perfect time. Even if you get off of the beat here or there. If you are rushing or dragging the tempo, that IS an issue and one that you need to address.

Personally, I wouldn't be spending my time or money on gear to hide the problem. I would take the money, get some lessons with a professional instructor, and work on having better time.

You also may want to examine the MIDI files to make sure that file doesn't have any unwanted tempo changes. I played in a cover band years ago that used MIDI for the backing tracks. On one particular song I kept feeling the music change tempo. It was slight, but it was driving me nuts having to adjust my playing. I kept telling the band and they just thought I was nuts and need to practice more. I finally convinced them to open up the MIDI file and check the tempos ... and sure enough, half-way through the song there was a unwanted tempo change that slowed the music down about 2 bpm.

If you start having the MIDI follow you ... yes, the drummer typically drives the band, but he's not the only one needing to have good timing ... you are going to make the audience nauseous. It will be like riding in a car with a driver who keeps pressing and releasing the accelerator pedal so the speed is 55, 56, 52, 60, 54, 59 MPH. I've ridden with someone who drives like that, and it makes me physically sick. I've also heard music that keeps changing tempo like that ... and people don't want to dance to it.

So again, I'm not trying to be mean ... just honest. You need to work on fixing the real problem and not some technical device to put a bandage or cover it up.