COM addins are a big security hole... imho. Allowing non-admin users to be able to install ANY COM addin is potentially giving them any/all access to your machine. COM addins can potentially do anything to your computer... with or without excel running. For this very reason... non-administrator users cannot install COM addins. It's not simply giving them access to making changes to the registry.
If you're unconcerned about security... why not make all users an administrator... if you are concerned about security... find another way.
You can do this with a simple script to deploy this across the network as administrator without having to physically sit at the workstation... or disrupt the current user. Here's an example:
First... download psexec on your admin workstation. This will allow you to start a process on a remote machine.
Second... create a batch-file that will do the work for you. Save it to a network share that the workstations will have access to. Something similar to the following:
@Echo Off
mkdir C:\Some\Directory\for\add-in
xcopy \\some\server\where\addin\is\*.* C:\Some\Directory\for\add-in
regsvr32 C:\Some\Directory\for\add-in\the-addin.dll
Third... remotely execute the file as administrator.
psexec \\some-workstation runas /user:domain\administrator \\server\where\bat\file\is\the-bat.bat
and voila. Dll copied to workstation... registered as administrator... and the user never had to log off... and you didn't have to sit at their computer either.