I downloaded the original media from here:
With /q option the downloaded MASetup.exe claims that it has the silent install switch /Q. It doesn't work. During install, the media is expanded to several files to users temp folder.
Amongst them are:
The expanded setup apparently installs either of those depending on if you have 32- or 64-bit Office installed, after that it seems to install some DirectX components if needed.
Unfortunately those above mentioned MSI's don't install directly - they claim to need the Setup.exe (which doesn't work silently with normal switches).
I opened MathematicsAddIns_x86.msi in Install Shield editor and looked at the Install Condition section. There were several. From there I could pick some properties that I used to try to make the MSI install directly.
And it works! For example, if you have Office 2010 32-bit installed and Windows 7 (which doesn't seem to need any extra DirectX components in this case), you can use just the MathematicsAddIns_x86.msi for the installation with the switches mentioned in the top of this post.