I've spent time on this for my last 3 reps, and had success.
Have found:
1/ Although these Ferrari keys with internals are the same frequency 433Mhz, as the Toyota MR2 Roadster, they're not matched to the same sub-frequency, so you'll have a challenge getting the car to recognise and program them to it (let us know if you have success with that)
2/ Its posssible to make the Toyota key internals (incl the immobiliser chip) to fit inside these genuine key cases, as I have done, also picked up a spare on ebay, followed the usual guide to getting the car to recogise, and now have x2 nice keys. In the pic below, the MR2 internals are fitted in the Ferrari key case, and the Ferrari internals are taken out (seen to the left of that pic)
3/ You'll need to modify the rubber key side by increasing the plunger size a wee bit on one pin, so it hits the toyota microswitch "on the button". As in the pic, I've done this and seems to work fine. You only need to use two of the buttons on the Ferrari key case
Hope this helps. Brilliant if you can get these supplied with the correct MHZ though, it'd save messing about like I have.