Kristen is proposing the cautious approach which does result in fewer disappointments. If plant survival is the most important consideration then wait for arrival at the new home and better weather before pruning.
A more aggressive approach that is still pretty safe is to prune the tallest stem or stems but leave a shorter stem that has lots of leaves untouched. That shorter stem will provide the energy the hibiscus needs while the pruned stems start to regrow. Pruning is good for hibiscus but should be done gradually a few stems at a time rather than cutting every stem at the same time. Also, look over our instructions on pruning on the HVH web site for details of how to prune. That page is
http://www.hiddenvalleyhibiscus.com/care/pruning.htmGood luck!
Charlie