A local VM on the Mac with Windows installed is also something I have seen in such cases.
I have installed PIM rich client via WINE on Linux just for fun before. It had some minor UI issues that I haven't noticed in Windows but it was just an experiment that wasn't worth troubleshooting.
If I recall correctly, WINE + the winetricks package (if it exists on Mac) are all it takes to get the desktop up and operational. It wouldn't hurt to also throw in playonlinux and/or lutris as they're also excellent for Windows support when it comes to gaming/more intense applications.
I run VMWare Fusion on my Mac with a Windows VM. It also helps to have a Windows versions of Excel for clients that have macros that only run in Windows.