I came up with a pocket solution that works for me.

I use velcro as the closure system on my kilts and run it across the entire inside-top of front apron.

I then made a pocket set out of leather that attaches to the velcro. It sits between the aprons.

This would be pretty useless to most of you - no velcro to attach it to - but the x-kilt makers might want to think about something similar in their next project... Or a piece of loop velcro could be added to the inside-top-outer-apron of an existing kilt is the owner didn't mind the cross of old-world and new.

Will post pics of my solution soon.