I have tried every way I can think of to implement this how you want to get it going, but keep running into road blocks like you have already seen.
There are a couple of options which aren't quite as nice to use, but will still get the job done:
1. Setting up the variables on one machine, exporting them and reusing them on another.
Adapted from how to set environment variable from file contents?
On a machine that has the paths setup already, run:
echo %PATH%> dat
This will create a file called dat which contains the full path from the reference machine.
You can then reapply them on a different machine by passing it into the command:
set /P PATH=< dat
It should be possible to edit
dat such that it only contains the paths you want to append to a machine and modify the command like so:
set /P PATH=%path%;< dat
Note that I have not tested this modification.
Going forward you could add any changes to
2. Using a third party app, pathed.exe
Using info from Edit the PATH environment variable in Windows without pain
Using Pathed, part of the gtools, you can append the path.
Assuming your list is List.txt and you're in the same directory as the list, the command would look like this:
for /f "delims=" %%x in (List.txt) do (pathed /append %%x /machine)
You'd also need pathed in your path or in the same directory you're working in.
2. Using PowerShell
You could also look into PowerShell, but you've already indicated this isn't an option (plus option 1 or 2 should be able to see you right.)