Is there a workaround I can implement for this?
We have a network segment that is Mimosa with an A5 access point and C5 radio's. Behind all the C5 radio's are switches and then customers who use PPPoE
The Mimosa's have been a constant pain in the ass and the biggest one is they don't even allow half of the frequencies in our country. The tiny selection of frequencies have all become totally crowded and unusable. The simplest solution is to throw the A5 in the trash and put in a MikroTik BaseBox5, set the C5's to 802.11 mode and hey presto. Problem though is Layer2 traffic does not transit beyond the C5. This would be because the frame header isn't carrying enough MAC address tags

Mimosa has very little to no configurable options, and the basebox is showing they don't support WDS (or maybe i've configured something wrong? WDS is enabled on the AP and set to dynamic, do I need to do anything else?)
Is there anything I can do - short of going and replacing all the SM radio's which is a lot of work and expense - to get Layer2 traffic across?

Did you find a solution to this ?

Yes. We went up to each and every Mimosa radio in our network, unscrewed its high quality hose clamp fitting and promptly turfed it into the nearest bin so as to not infect any potential eBay 2nd hand buyers with deep regret and seething hatred. We then fit MikroTik/Cambium/Ubiquiti and lived a better life

Why Mimosa has 802.11 support without WDS (or MikroTik's MAC Masquerading) is monumentally stupid. Why is the point if you can't attach anything behind it
Amongst many other issues we've deemed them little more than cancer transmitters (not even great at that, they'll probably fail too soon) and will no longer use them