I'd suggest you send the ECU, and someone (Ed?) opens it and solders the Nistune board in. - If I read the instructions correctly, it's possible to install the board and leave the original map (by not changing the jumper); you can then "activate" the Nistune board when you're ready to tune.... or you could just as for the base map to be put on the board until you're ready to tune it.
I did have a look at trying it myself (i.e. buy the board and install it), but I don't have a de-soldering tool to do it correctly.