If I need to collect a parcel, providing it isn't massive and heavy. I take my Brompton to the collection office, fold it up and take it in.
It is is something big, then its the CC and I just bungee cord the package to the rack. The Fulham collection office has a bike rack for the postie bikes and staff I guess, and I just use that. They have never told me not to use it. There is a railing, but there is a sign telling you not to chain bikes to it.