If you're still looking to do this, these guys make a dongle to control the accelerator pedal with faked human inputs.
I'd bet a Tesla would reject it into limp mode. It's definitely not as simple as throwing a few DACs in place to get it to fully control the system like this. Tesla has done of a lot on the hardware side of things to prevent such an issue or attack on the system. This might work on other vehicles, but you won't get a full launch out of a Tesla with that hardware.