How can I dynamically load and unload .Net assemblies inside a WCF service

Question

I want to develop a windows service hosted wcf web service that would behave as a task execution management and reporting service. Each task would be represented as a .net assembly, the task name and dll path would be in a central configuration. The task would primarily have a Execute and a Stop method at the very least. It should be possible to load, execute, stop and unload tasks while the wcf service is running and other tasks are running. One instance of each task can be running concurrently. One task having an exception should not abort other tasks. I am thinking of methods like

[OperationContract]    
bool Load(string taskName);
[OperationContract]
bool Run(string taskName);

I am thinking of how I can accomplish this loading and unloading tasks on demand as well as the isolation. Some options would be using Reflection, MAF (System.Addin) etc. The initial performance hit to load is acceptable as this load/unload would occur very infrequently.

What is the best way (library, api, framework etc) to achieve this goal.