Hairpins might work if the comb was more than several years old. Your comb is not a year old and hasn't had a chance to be toughened and thickened up by the bees as would naturally happen after a few years in an active hive. Incorporating some cotton string, like butcher's string, along with the hairpins is probably a better idea. The cotton string supports the comb giving the bees a chance to make wax and attach it perminently to the top bar. Once the comb is stablized, the workers will chew up the cotton string and drag the fibers out of the hive. Were the zip ties for vertical stability and to be cut out later? If so, maybe a half inch wide piece of corrugated cardboard would have given the fragile heavy brood comb some bottom support so that the zip tie didn't cut through the comb from the downward weight of the comb. The workers would chew that up and drag it out in a few weeks also just like they do with the cotton string. Wrap the cotton string over the top bar, down over the comb and under the bottom cardboard support strip, then up again and over the top bar forming a helix to support the length of the comb. This helps comb hang fairly vertically below the new top bar. These methods have worked for me whenever I transferred bees from a Honeytree or a building wall into a Langstroth hive. No matter what, it's always a messy traumatic job especially for the bees.
Keep trying, it'll work! The bees will do their things in spite of us beekeepers meddling in their methods.
Just a few thoughts from a former beekeeper - Happy Easter!