rp_filter equivalent?

Hi all.

I'm wondering what the equivalent to the Linux rp_filter is on FreeBSD. I'm
asking because I've got a set-up on a hosting provider where I have a
floating IP address that's not related to the main IP address of my system.
Which is to say, my system is a.b.c.10 and routes through a.b.c.1, and I've
got a floating IP that's x.y.z.50. Traffic from that x.y.z.50 address is
supposed to route through a.b.c.1.

I've got a vnet jail that's set up to use that x.y.z.50 address, and I've
assigned x.y.z.50 to epair0b in the jail, but I ran into a problem. I
couldn't tell that jail to use a.b.c.1 as its default gateway and that that
was out through epair0a without assigning an a.b.c address to epair0a, even
though I don't actually have a spare assigned to me.

I believe I can just tell Linux to ram packets out an arbitrary interface
if I turn off rp_filtering via a syscall, but I'm not sure how to cleanly
do this with FreeBSD, hence my resorting to pilfering an IP address. I'll
never receive traffic intended for this pilfered address and there's no
risk of it causing confusion, but it doesn't feel like a clean answer.

So, there's my question: is there some way I can have my vnet jail send
packets out an interface that the system believes is unrelated to the IP
address assigned to that interface?

Thanks!

-- 
(defun main () (format t "Mason Loring Bliss  -  mason@blisses.org - ")
 (format t "By the mysgydynge of the sterysman, he was set vpon the pylys")
 (format t " of the brydge, and the barge whelmyd. - Chronicle of Fabyan~%"))