Hi Chris,
Thank you for your interest in Syncfusion products.
It can be done done by handling the MouseUp and MouseDown event in GridControl and the AllowSelection must set with AlphaBlend. I ahev attached a sample that illustrates this better.
Refer the sample form below link:
http://files.syncfusion.com/support/samples/Grid.Windows/7.3.0.20/Forums/GridSelect.zipPlease let me know if you have any queries.
Regards,
Lingaraj S.