Support for AddPath has been added in the 7.22 release, but the intended behavior is unclear.
I’ve noticed it does send the peer multiple active paths (ECMP), but it doesn’t send candidate (inactive) paths. For a Looking Glass application, it would be essential to send candidate paths, too.
My BGP connection’s output filter is a simple accept, so it’s my understanding that it shouldn’t be filtering only by active paths. I looked into whether it would be possible to force-select inactive paths too by using Select Rules, but I found no way to do so – not sure if it’s even possible, seeing as how Select Rules aren’t really documented.