OK, I did this:
1) I deleted the tags file from HEAD, 1.9 and 1.8 (all currently developed versions)
2) I added a tags.txt file which includes directions for creating the tags file or downloading it.
3) I added "maketags" to the moodle-cvsupdate script on download.moodle.org.
As a result:
a) The latest tags file will be included in all the weekly packages
b) The latest tags file is always available from the download server:
http://download.moodle.org/tags (for head)
http://download.moodle.org/stable19/tags (Moodle 1.9.x)
http://download.moodle.org/stable18/tags (Moodle 1.8.x)
(so you can easily get it with wget etc)