Magic of cloning is the only solution. Where the clones of main body are made that are perfect replicas, and ala "speed learning from Naruto" - they transfer feelings and experiences back to main body after spell ends - so that all the first time sex feelings and experiences move to the dude.
They could still fight about who gets the "real" one, or out right refuse this solution and chose to be in turns?
As a side note - start of this chapters seems to indicate that all the girls in MCs harem were victims of some kinda tragic stuff including rape (the basilisk one I think), and MC probably saved them from darkness/depression/stuff and thats why they are so psychotic on being with him - extremely strong suspended bridge effect of sorts?