I think it may be possible to harness yet another Araneaean characteristic for the spiderbots.
Those loosely aggregated “piles of rubble” could be webbed.
If the pile is rotating slowly, the spiderbot could play out its fiber, gently wrapping the rubble to keep it together. Or the bot could orbit the rubble-pile.
Later, strong tethers could be arranged to allow towing and maneuvering, very much as you described.
It would be interesting to see a gathering of spiderbots, arms linked together like skydivers, bringing a load of loose boulders along to their fiery rebirth as an atmosphere somewhere.
Evening, y’all. Happy Friday!
Heck, it wouldn’t be too much to have them exude aerogels to insulate loads after webbing them.
That way, frozen liquids would be preserved, even if they tried to sublimate.