Source address selection algorithm w/ bgp

Hello
Hi misc@

What is the current canonical way to tweak source address selection?

I have a bgp multi-homed router, and while answers do use the correct
source address, host-generated traffic uses the outgoing interface IP
address:

$ route -n get 194.2.0.20
route to: 194.2.0.20
destination: 194.2.0.0
mask: 255.255.192.0
gateway: 44.151.211.1
interface: em1
if address: 44.151.211.2 <<<< Not reachable from outside my network.
priority: 48 (bgp)
flags: <UP,GATEWAY,DONE>
use mtu expire
3 0 0

This can cause issues when the /30 peering subnet is not announced, as
return traffic (or even forward w/ urpf enabled in adjacent networks)
will be dropped.

thanks in advance
--
pierre