BGP neighbors and the remove-private-as command

Imagine you have a BGP router with a public AS number. It peers to a BGP router with a private AS number which in turn peers to a BGP router with a public AS number.
ie.
R1(AS 123) -> R2 (AS65000) -> R3 (AS 456)
On the final router (R3) you want to peer with another router with a public AS number and you want to remove the private AS from all routes.

I've tinkered around and can't find a way to do it. If you configure BGP on R3 similar to this:
router bgp 456
neighbor R4 remote-as 789
neighbor R4 remove-private-as

The prefixes from router R2 are advertised to R4 with an AS path of 456. The prefixes from router R1 are still advertised with an AS path of 456 65000 123. The reason for this is that the remove-private-as command sees the AS path as already having both public and private AS numbers and considers it a configuration error. Therefore it does not remove the private AS number.