Instead of going back to PHL on part 1/2 of ticket B, go someplace else. There is nothing wrong with doing an end-to-end as long as you meet the minimum stay requirements. So, try:
Mon morning - PHL->XXX on part 1/2 of tix A
Mon evening - XXX->YYY on pt 1/2 of tix B
Tue morning - YYY->XXX on pt 2/2 of tix B
Tue evening - XXX->PHL on pt 2/2 of tix A
where XXX is ATL or some such place and YYY is anywhere cheap with no minimum stay requirement that is not ATL or PHL. I assume that your previously proposed PHL-ATL has no more than a 1 night minimum stay requirement?
Comments? Russ?
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Time..... is on my side.