I have two transit providers, A and B. The business has chosen to make provider A more attractive due to billing concerns (we get attractive bulk pricing from this global provider). This was done by a combination of AS pretending for ingress and local preference. As expected a bulk of the traffic goes through A unless it has an issue.
There is an obscure ISP that we need to reach which happens to take a substantially better route through provider B. While I can certainly alter the traffic on egress, on ingress BGP will just "do it's thing" and the prepended route will look less attractive meaning return traffic will go through provider A.
My goal is to have most of the traffic go through provider A (preferred) except for this one AS.
How can I engineer around this problem?
Edit: I apologize I did not provide the router model as I preferred to frame this as a generic routing question. The router is a Juniper MX204. The part I'm really stuck on is how can I ensure return traffic, only for this ASN goes through provider B and not A.