Need previous version of Controller for older MacOS

Greetings,

I've got an older iMac operating on 10.12.6, and I just installed the latest BluOS controller 4.2. Unfortunately I didn't read the fine print beforehand, and it isn't compatible with the my old OS.

I've searched around, and it looks like getting the previous version BluOS isn't so easy.  I don't have a recent enough Time Machine backup to be useful in this instance.

Short of buying a new computer, what are the options?  

Thank you for your help!