Announce less specific prefix in routeserver environment for upstream purpose

Dear Bird Users, I have the following setup: Peer1 - AS65001 Peer2 - AS65002 RS - AS65123 GW - AS65123 All are connected via a layer 2 infrastructure and share next hop addresses out of a /22. This /22 is part of a /20. RS works as a routeserver with "rs client" in the protocol definition of Peer1, Peer2. My goal is, to announce the /20 over GW to the routeservers GW hasn't the "rs client" option set but "gateway direct". To solve the iBGP and empty AS path of GW, I want to prepend AS65123 for all GW incoming prefixes, so that the as path isn't empty. Do you expect this as a working design to announce the /20 from GW via RS to the peers? Rgds, Stefan