Calling it in should work. There are some really annoying gaps in the online booking tool - of course AE will not do anything about it as it gives them an extra $30 every time someone needs to call in.

Just last week I was playing with itineraries to find flights that would work for me (knew I'd have to call in regardless as it was complicated-ish), looking up YVR-JNB as a one way turned up a single classic fare option in PE/J on my date (YVR-DEL-ADD-JNB), but if I changed it to search YVR-DUR the ONLY options were suddenly via LHR and only as priority fares (double points). I found a separate leg JNB-DUR that fit in beautifully time-wise and when I called, YVR-DEL-ADD-JNB-DUR wasn't an issue at all.