Not sure which kind of receiver you are running, 5.1, 6.1 or 7.1 but assuming the worst case scenario (5.1), you can just buy a speaker splitter. Don't "cheap out" though if you are wanting to run Bose speakers. Buy something mid-to-high end because you will notice a difference.
Then, take a 3-foot piece of speaker wire the same guage you are currently using on your HT speakers. Now, disconnect your left and right surround speakers and connect them to the 'A' speaker terminal on the splitter. Connect your Bose speakers to the 'B' speaker terminal. Now, connect the splitter to the receiver using the 3-foot piece of speaker wire and voila!
When you you want to use your HT, select speakers 'A'. When you want to rock out on the deck, select speakers 'B'. And, if you really want to, you can have both sets on at the same time but you will only be getting 1/2 power to each set.