One thought on twisting the linen, and I imagine that there is a better way to do it. Twist it together like the bow makers do when they are twisting sinew to make a bow string.
The tricky part would be that one would have to unravel 150' of both lines before the twisting began. That would surely cause a tangled mess.
Altho, there might be a way to do it before hand on two smaller spools.
The bow maker would take 2 strands of sinew, tie them to an eye hook that is screwed into a piece of wood. The other end would be tied to something as simple as a hook fashioned from a piece of coat hanger. The wire would be chucked into a drill chuck. Spin the drill.
Of course, like I mentioned, the bow maker is working with 2 much shorter pieces of sinew.
Figure out how to unwind 2 150" strands of linen and that might be one way. You could also wind them right off the two spools together but you'd
have to figure out how much line you have out and twisted together.
You could wind 2 - 150' pieces onto two smaller spools and then wind those together afterward.
Much hassle so would easily be at least 2 to 3 times the normal cost of a wrap as was stated previously.
Edit - See what happens when I start thinking. If you were to tie the other end, you would have to have a pretty long shop.
There might be a way of fashioning the drill chuck hook to be able to hook both pieces of linen close to the first eye hook. (An L shape) You'd then have to work backwards from the eyelet to the two spools.
Or better yet, call Cortland Line and ask them how the heck they do it. 250 K later. Hahaha.