I am sure this is not a new idea, but hey, new forums.
Interbus can’t have an LP store because they don’t have any stations.
Why not use the CONCORD LP model and simply allow exchange of Interbus LP with standard high sec empire LP stores at a 4 to 3 ration (or less even).
Interbus agents do get used by folk that do not want to trash standings seems a bit mean to deny them their LP as well.