Excel XLAM synchrnoize local version with network version

I have several Excel add-ins (XLAMs) that I normally save as read only instances on the network to allow users to access but also allow me to update when needed without worrying about whether or not any of the users have the file open.

That all works fine.  However, I now have users who want/need to be able to have access to the XLAM addin when they are not able to connect to the office network.

So what I would like to accomplish is the following:
1 - have the ability to have a local copy of the XLAM that can reside on the user's local drive for them to utse when they are off the office network
2 - but have the ability that the XLAM can (when on the office network) check the network location to determine whether or not it is the latest available instance and if not download a copy of itself down to the local drive.
Since i expect that it might not be possible to easily download a copy of "yourself" to the local drive to overwirte "yourself" while running, I'm thinking that perhaps i need to have a separate local file whose only job is to do this comparison of the main xla to determine if a newer copy of it should be downloaded to overwrite the old one.

What is the best way to achieve tihs functionality for when i have XLAM logic that needs to be regularly updated but which users do have a need to have access to when not on the network?  Would my above approach work? and if so, does anyone have suggests as to how to best have the local copy be able to check whether 1) if the network is even available or not and 2) if it is the latest version?

Thanks for any help!
Shelly