Complicated API issue with dynamic assembly calls

I have an interesting challenge I am wondering if anyone here can give me some direction.

I am writing a Windows Forms application that runs on the web and uses SQL Server to save and pull data.

I want to offer a mini "plugin" API where developers can create their own assemblies and implement a specific interface (IDataManipulate). These assemblies can then be used by my application to call interface functions and do something.

I can create assemblies using my API, copy the file to a folder on the local hard drive, and configure the application to use Reflection to call a specific function from the implemented interface (IDataManipulate.Execute).

Problem:

Since the application will be installed on multiple workstations on the network, it is not possible to copy the plugin DLLs that users will create for each machine.

Solutions I have tried:

Solution 1
Copy the API DLL to a network share.

Problem:
Requires AllowPartiallyTrustedCallersAttribute which requires chanting .Net which I cannot force from my users.

Solution 2 (preferred)
Serialize the dll object, save it to the database, deserialize, and call IDataManipulate.Execute.

Problem:
After deserializing, I try to apply it to the IDataManipulate object, but it returns an error looking for the actual dll file.

Solution 3
Save the dll bytes as byte [] in the database and re-create the dll on the local PC every time the user runs my application.

Problem:
The Dll may have dependencies that I don't know if I can detect.

Any suggestions would be greatly appreciated.

thanks