I would think you could make some custom filters based off what it looks like.
https://www.w3schools.com/tags/tag_base.asp
Since it says it is usually href or target, you could look for these in the message body.
<base
For less false positives, you could use these.
<base href=
<base target=
Seems like any use of the base trick uses one of those 2 code.