Some random ideas off of the top of my head:
Is this a solo encounter or will they have other enemies to keep them busy until the Golem breaks free? If so I'd have the Golem actually doing damage to the scaffolding every round in an attempt to escape, in addition to any damage being done to it by the PC's while trying to free him. (though if they're distracted by other enemies I doubt they'll be doing much damage to the scaffolding, just the other enemies)
Another option: Make him a bit of a hazard. Every round on his initiative anyone on the scaffolding has to make a balance check or fall prone, if they fail by five or more they are slid one square and then fall prone, in the direction away from the Golem, possibly allowing you to knock PC's off of the scaffolding. (then maybe a save to see if they hang on and can pull themselves back up, you know, action movie stuff)
This only works if the PC's have something else to focus on for the beginning of the fight mind you. Maybe the Golem's creator(s)/minions? A savvy player may be able to damage the Golem with a Thievery check in order to eliminate a specific attack or slow it's movement, that sort of thing.
And having other enemies for the PC's to focus on until the Golem breaks free seems like a good idea just from the fact that they will likely just be standing their slashing at it, possibly using all of their dailies on this enemy before it even breaks out. The idea alone is amazingly cool and I'll likely be stealing it.