POLICY changes are needed.
1. first question asked of customer is 'Are you drinking your coffee with us today?' If drinking in, the customer gets a mug. AND a freebie of sorts (free croissant or cookie. Whatever)
2. reward customers for drinking in with a reward card.
3. introduce THE PAPER CUP CHARGE which makes using a paper cup more expensive than a thermal or ceramic cup.
4. give away free thermal mugs
5. if that's too painful, give them away as a reward for drinking in
6. just give them away.
7. or give them away for a very small charge. In China the thermal cup cost is about RMB10-20. If purchased in bulk, the price comes down significantly to maybe just RMB5. Imagine the discount if you're putting in an order for millions.
8. Make 'reduce paper cup usage' a KPI for store managers. Charge them if they use too many. HAve targets and intra store competitions for the store which uses the least and reduces the use of paper cups. REWARD big time.
9. make it a KPI for GM's, Country Managers, Regional Managers.
10. Make it a REVOLUTION in the company.

And while you are at it - work on reducing the wooden stirers, plastic knives and forks (Coffee Bean and Tea Leaf offers drink-in customers metal spoons! Nice touch. Wood is sooo nasty)

I now carry my own metal spoon and the staff are really happy to blast it with the steam to clean it for me. They like it!