Diplomatic approach to clients with badly set-up monitors

This is not a technical question, but a matter of client management. (I edit on Final Cut Pro and always do the gamma adjustment on final output, since most videos are still viewed on PCs. So, technically speaking, I think I'm providing the best product I can.)

Most of my work, both the rough cuts and the final output, is evaluated on my clients' own computer monitors.

Problem: clients don't use color bars to set up their computer monitors, which vary by a huge amount in their contrast/brightness/chroma settings.

I was wondering whether anyone else has this issue. I have been thinking of offering my clients a monitor set-up utility, but that seems a little intrusive and obnoxious.

My clients have not actually complained about any issues of brightness, but on my own range of PC monitors, the same video can look too-light, perfect, and muddy. So I'm concerned.

Bob C