Hi Greg,
Thank you for your interest in Syncfusion products.
Please try using CustomerComparor in GridGroupingControl Sort/Grouped column to achieve your requirement as shown in attached sample.
Refer the sample from below link:
http://help.syncfusion.com//samples/Grid.Windows/GGCSamples/GGCGroup/main.htmPlease let me know if you have any queries.
Regards,
Lingaraj S.