Edit: Although making a basket to sit in as a crude elevator shouldn't be that hard. People did it all the time in the middle ages.
Yeah, the construction should be doable, but getting the materials could be tricky. Pan has 1 structural junk but that probably wouldn't suffice. I guess we could cannibalize the bore a bit in a pinch (I'm sure we can find an armor panel somewhere that isn't strictly needed as long as we don't do any more drilling) but that's basically subterranean heresy. Or we go to the nearby settlement and see what we can scrounge up.
Although now that I think about it, it's not really necessary, you can just tie people to the end of the rope and lower them down.
This gives a hilarious mental image. Just a bunch of unlucky people tied together resembling a neat bunch of grapes. And then the star dragon realizes he hasn't had second breakfast* yet...
*yes, the star dragon is a hobbitEdit2: And really, with the rope method you have less chances of encountering the dragon since you'll both be moving more quickly and you'll be going through the center while the dragon circles around the ruins.
Are you sure it'd go quicker? There'd be more distance to cover vertically than horizontally, right? Another possible downside is that the people being lowered won't be able to do much outside of maybe shooting or diving, while people moving over a bridge might be allowed to try and sneak to avoid the dragon's gaze or get a dodge roll if it decides to do something.
On the other hand, if the dragon is indeed moving in a fixed pattern and not going through the middle (and doesn't react much to our presence) then it probably is the safest option all in all.
Talking about that, Lokam does have Caving skill and moth wings. If we need someone to get to the other side, he could do it.
While throwing moths in head-first by way of experimentation has my vote by default it might be safer if we try chucking a large rock inside the room first to see if it responds to it in any way, assuming our various "observe worm" actions don't give us any good intell. We still have plenty of time in-game, there's no need to rush in overly hastily.