Groove Matrix limitation with loops starting with a pickup?

Is there any way to have grooves in the groove matrix begin before the beginning of a bar? IOW, many of my patterns begin before the 1... with a pickup... usually a few 16th notes before the 1. AFAICT, there's no way to use them in the groove matrix because grooves always start on the 1 in the matrix. I've mickey moused a few patterns by having a blank measure at the beginning of the pattern with the pickup at the end, but that's a less than desirable solution for me most of the time. Does anyone know a way around this limitation of the Groove Matrix?