This one didn’t take too long to figure out. A little time with Google and I found the solution. There’s a little perl script that came with MythTV that will create an XML file that mythfilldatabase can use to put the icon information into the DB. It ended up just being two commands, though there are a few holes (mostly local stations). Anyway, here’s what I had to do (because I installed from an RPM my contrib is at the path below):
$ perl /usr/share/doc/mythtv-0.18.1/contrib/mkiconmap.pl Answer the questions $ mythfilldatabase --import-icon-map iconmap.xml --update-icon-map
And just wait for it to run!