thread impersonation

[Gonzalo]

Hello guys.

I'm new in freeBSD and I'm looking a way to impersonate threads in FreeBSD.
In Linux I did that with setfsuid, but that only work in linux and is not
portable :(

I saw that in FreeBSD there is Jails, that could work? Is possible to create
a Jail for every new thread and "impersonate the Jail"? Maybe I'm saying
things without sense :(

Thanks in advance ;)
Gonzalo