The best way would be if you can have a simple click track on a separate output that only the drummer can hear either through headphones or a dedicated monitor speaker. That is the best way for him to hear the click track over his acoustic drums.
I play in a band with a drummer using a Roland V-Drums electronic kit so it is a little easier because he already has a monitor system for his own drums. We use a few sequences and I simply have a hihat click running through the song. He can hear it but the audience don't notice it along with his own hihat and drum sounds. I always have a bar of the hihat at the start of the song to count us in and the whole band can hear that. If the drummer has the click isolated in headphones then you would want to have 2 bars of count in, 1 bar for the drummer and another bar for him to count off with his sticks for the band. Because my band can hear the click we only have one bar count in.