Hi Bastien,
If my understanding is correct, you want to creat a sort of "port pool", so when a packet comes from inside to outside, you assure that it's source port will be translatated to a specific defined range. Is that?
Unfortunately this isn't supported. You can surely restric the ports that will be translated, but you can't restric to what it will be translated.
Let me know if this clarifies.
Thanks,
Pedro
