openssh support for selective port-forwarding on a per-key basis?

[sen_ml_(_at_)_eccosys_(_dot_)_com]

i know how to forbid port forwarding w/ the "no-port-forwarding"
option in the authorized_keys file, but i'd like to be able to specify
on a per-key basis exactly which ports can be forwarded.  this is not
currently possible, is it?

are there any plans to add an option to the authorized keys format to
allow specification of exactly which ports are allowed to be
forwarded?