Lichess Swag Store Username Customization

I would love to support Lichess via swag purchases while also directing people to challenge me. If possible, it would be a great option to add username details to your swag purchase for an additional fee. So the front of the shirt would say Lichess.org and the back would say "Challenge me @nguytravis" or equivalent.

Unfortunately the vendor (spreadshirts) doesn't have this as an option.