You can use Policy Based Routing (PBR) for this. The standard configuration would be similar to this:
1) Define an ACL for Citrix traffic:
access-list 101 permit tcp any any eq 1492
(you can enhance this with your specific IP addresses instead of "any").
2) Define a route-map:
route-map Policy_Citrix permit 10
match ip address 101
set ip next-hop dialer0 f0/1
route-map Policy_Citrix permit 20
(this will send the Citrix traffic to dialer0, and if dialer0 is unavailable, to f0/1)
3) Define policy routing on your LAN interface (where the Citrix traffic originates:
ip policy route-map Policy_Citrix
You can also add more intelligence to PBR by tracking the reachability of certain IP routes (see http://www.cisco.com/en/US/products/ps6599/products_white_paper09186a00800a4409.shtml).
This will only redirect inbound (from your remote LAN to the Citrix server) traffic. You need a similar PBR configuration on the router which routes the traffic from the Citrix server back to the remote LAN.
HTH, Thomas