Hopefully others who know coding will be able to help more with this issue but in the meantime, I did have this thought. I was thinking a work-around solution might be this:

Set up the minimum order fee and then after the first order, give your customers a discount coupon for that amount for future orders. You could choose not to issue the coupon if you thought they might be "granny" type buyers or give it to everyone - if for everyone, could include it in the order confirmation to make it automatic.

Not a perfect solution as it requires the buyer remember to claim the discount for next orders but might satisfy the boss until you come up with a more elegant fix or you can convince them to tackle it another way.

cheers
Leah