I don't know if it will work with hops, but here in Northern Maine (46th parallel), when a light frost is coming on, we'll cover stuff that's sprouted with bed sheets.. if it's a heavier frost, we'd cover them with a bucket or a cut-off milk jug...
Another option would be to take some of those bamboo "hoops" (they look like an upside down "U", and some vinyl sheeting (contractor's plastic or shower curtains, etc) and make a sort of little greenhouse over them.
And I'm in the same boat hillhouse is in.. still too cold here to put the rhizomes in... but half our regular garden is about planted..