The "solution" - in that it clears the log - is actually in the original post, as is the root complaint of "we need a way to issue an SEL clear from the GUI." But that isn't any more of a "solution" than sticking a piece of tape over your check engine light, Homer Simpson style.
The system event log is trying to tell you something - maybe something important, like "ECC threshold exceeded in DIMM_A1 - replace it" or "your CPU is overheating and thermally limiting itself" and simply muting the alarm isn't going to solve that, which is what I believe was trying to be said. (Perhaps a bit bluntly and out of frustration from the "me-too" posts, I'll admit, but the intentions were good.)
If there's a particular hardware bug that causes the SEL to fill itself up with false-positives, that's also something that needs to be addressed, otherwise you end up with "alert fatigue" and potentially miss a serious issue.
You can also set the threshold to "never alert" on the low space specifically, by going to System -> Alert Settings and setting IPMI SEL Low Space Left = NEVER
but if your system doesn't cycle the oldest alerts out (or floods them so quickly that it pushes valid errors out) then you run the same risk of missing something important.
Cheers.