This is a very good question and one which is asked several times a month in the forums.
The short answer is that you just get a switch which does not connect to the fixture, usually intended as part of a “virtual three-way,” tie off the line to the fixture so that it is always powered, and use the auxiliary switch on the wall. It will look just like a regular switch but it will not turn the current on and off to the bulbs. Instead, it sends a message to the hub which then sends a message to the bulbs. The gocontrol WT00Z is very popular for this purpose.
For additional details, please see one of the two existing FAQs:
