。。
There aren't any other positions left anyway. All that's left is regular member.
Literal
Other [attributive-の] positions [dismissive-なんて] not-remain-[reason-し]. Rest [topic-は] regular-member [only-だけ] is-[assertive-よ].
~し at the end of the first clause is the listing-reasons particle — 'and also / besides X (so Y).' It often leaves the conclusion hanging, inviting the listener to infer it. ~なんて dismisses 'other positions' as unworthy of serious consideration. 平部員 ('rank-and-file club member') literally 'flat member,' where 平 means 'ordinary, unranked' — cf. 平社員 ('regular employee') in the corporate world. あと here is 'the remainder' (not the temporal 'later').