Ha.....You are an Evil Capitalist
So offer "Winter Conversion Kits"
Scissors...threads....needle....appropriate color and texture cloth.
The army often goes from long sleeves to rolled up short sleeves in its working uniform, so some ingenious individuals put Velcro loops on the inside of the top of the sleeves and outside of the lower sleeves. In either case it is invisible to others so does not violate uniform standards.
It works best for those with broad upper arms, that are constricted by rolled up sleeves.
Wear a long sleeve underneath it.