Wildcards in proxy bypass list
Looking at this CyanogenMod source code (which, according to the file history, does not actually have any CyanogenMod-specific changes), I see that the initial dot in proxy bypass list elements is just ignored, and an initial wildcard is implied — that is, you can write either example.com or .example.com in the list, and this entry will match example.com, a.example.com, a.b.example.com, … (note that any number of subdomain levels can be matched, unlike, e.g., with *.example.com in an SSL certificate).

If your phone does not actually work this way (e.g., you add example.com to the proxy bypass list, but www.example.com still goes through the proxy), either this code was modified by the phone vendor, or a particular app is using its own implementation of bypass list matching instead of the system-provided code.