[spc476]

I can see it as a bootstrap method. You attach a string to the inside end of the vine that moves forward, and it spools out as the vine "grows":

    ____________________
                        \
    O=string============+   movement of growth ->
    ____________________/

        O = spool of thread

When you see the vine on the other end, you can open the end to get the string, attach the cable to the former spool end, and start pulling the string to pull the cable. You want a light enough string for the vine to pull through, while being strong enough to pull a cable through.

[LostLocalMan]

To affix your spool, or to access the string at all you need to go through the airtight robot and you need to know the exact distance that you need to run the wire since you can't access it unless the robot is fully extended. Kinda only makes sense if you have exact measurements and are willing to destroy the robot after it fully extends. Still probably a great way to run wire through long pipes.

[psd1]

Another possibility is just to leave the appendage of the robot in place. It's some form of inexpensive polymer, PET perhaps.