Can 'Free shipping' exclude other discounts?

Site URL: https://www.oliverjwoods.com

I would like to run a free shipping offer at the same time as a subscriber 10% discount. 

But is there a way to prevent users from combining? Ideally allowing them only the bigger discount — for example if the free shipping is a better discount than 10%, then they automatically get the free shipping.

Thanks in advance for any pointers!

I'm afraid it can't be done with Squarespace

Thanks Rob, I thought as much

This is very annoying, Squarespace. I hope you think about changing this! It's very restrictive for small businesses.