If your storage Container Field ia in a separate table, you could create one record for each platform, and store the correct plugin version in each record's stored field without needing a second field.
Then script the plugin installation with a find for the OS-appropriate record in the plugin's table.
Thanks for your quick reply. One more question, is there a calculation to determine if the user system is 32 or 64bit in machines running Windows? Alternatively, would the 32-bit plugin work well in 64 machines?
In terms of the BaseElements plugins, their 64 bit is only for Server, not FM Pro so 32-bit is fine for 64 bit OS.
Also they have on their blog an example file on auto installing either their BaseElements Mac or Windows plugin (it is an old version included in the example).
Thank you very much for your help.
Also note that there is a bug in the 2.2.x release that prevents it loading on windows. It's fixed in 2.3.0 which is the current release.