Maybe I'm misunderstanding something, but why not apply a layer of tape immediately on top of the conductors - since a thickness of .X of a mm (through) will insulate 22KV, Y mm (across - where Y is the distance between the conductors) definitely ought to do it. Although there is the glue that holds it down - I wasn't sure if that was the glue you were referring to, or if you meant some other glue - that might not be as insulating (or maybe it is, just don't know). But, anyway, if the glue might be an issue, you'd have to apply the tape non-glue side down (and stick something like regular electrical tape to it, glue-glue, to nullify its glue on the now-up-facing side - unless you want to use that to join the two layers of the original together). As to how to get it to adhere: if you can figure out what the insulating glue was that they used originally, or some modern facsimile thereof, you could use that.