Ideas to consider:
Each month, have a Shitpost Roundup on The Universe of Discourse
with a menu of the previous month's shitposts. Then people who
follow the main blog can find out what went on, which might be of
passing interest, without actually following the shitpost blog,
which probably isn't.
Instead of trying to get posts into the right place the first time
around, just make a monthly pass over the shitposts and see if any
should be promoted to The Universe of Discourse. This would be a
good opportunity for additions and emendations.