change pool or node in existing APM session

APM 11.5.3 HF 2, reverse proxy for OWA with SSO via NTLM etc. working fine.

Now users click on Enterprise Vault link in OWA/Exchange and get a redirect to the external OWA link with new path (https:///enterpriseVault/).

Must send the request to the Enterprise Vault server now.

1st try: create new pool for Enterprise Vault, read out path in HTTP_REQUEST and assign the new pool via iRule (see below).

2nd try: include Enterprise Vault in OWA pool, read out path in HTTP_REQUEST and assign the node via iRule. Use priority group to make sure Enterprise Vault server is not assigned in OWA pool member selection.

=> both does not work, logs show me that still the OWA pool or the Exchange node is assigned, and I get a "404 Not Found" back from the Exchange server (which does not hold the Enterprise Vault ressource).

3rd try: assign new pool via LB::reselect. => not valid in HTTP_REQUEST procedure.

Any idea how to send this request to the separate Enterprise Vault server?

when HTTP_REQUEST {

    switch -glob -- [string tolower [HTTP::path]] {
        "/enterprisevault*" {
            pool /P-CUST/PL_CUST_MAIL2_EV_rd90
            log local0. "Client (maybe not) redirected to EV, Host: [HTTP::host], Pfad: [HTTP::path], Pool: [LB::server pool], Node: [LB::server addr]"
            return
        }
        // other switch statements omitted
    }
}
when HTTP_RESPONSE {
    log local0. "Return packet from [IP::server_addr], Status: [HTTP::status]"
}