7yds of 60" weathered black watch

[Damocles]

The sort of thing you are describing is a tailors padding stitch,many of the traditional kiltmakers use this at the back of the on the cutout portion of the pleats to secure all the loose bits and it helps to stabilise and secure all the remaining cutout parts. When finished the whole back of the kilthas effectively become one piece of fabric again,and looks at bit like this

I'm sorry , but I don't think it would work very well in trying to thicken up afabric that is a little (or a lot) to light for a traditional kilt, any fabric that is less than 11-12 oz is really on the edge of being useful of kiltmaking ina traditional sense.Having to pad the entire length of fabric would be a major undertaking, and padding stitches are most often used for areas that need stiffening such as collars, and like, not for complete areas.
Sorry to be the bearer of this news...

nope that's not what i was talking about. i was talking about a fiber conservation technique called "Mounting". were by two pieces of fabric are joined back to back using a hidden internal stitch that can not been seen from ether side. its also used some times in dress and suit making when you have a piece of fashion fabric that is to light for its intended use or were body is desired with out shaping. its like pad stitching that you are describing but instead of doing on the back side its done between the ceprit layers to mount them together. this is done in museums all the time to conserve tapestry, clothing,and many other types of fiber that are to fragile to hold up under its own wait normally a muslin is used but it can be done with any kind of fabric. in this case i would recommend Wool it would make the care much easier.
Ps i did say it was a lot of work and it was more of an academic comment rather then advice on what i think he/she should do