Visual Studio 2008 locks custom MSBuild Task assemblies

I'm developing a custom MSBuild task that builds an ORM layer, and using it in a project. I'm being hampered by Visual Studio's behaviour of holding onto MSBuild task DLLs and not letting go.

I'd like to organize my solution like this;

My Solution
 |
 +- (1) ORM Layer Custom Task Project
 |  |
 |  +- BuildOrmLayerTask.cs     // here's my task
 |  
 +- (2) Business Logic Project  // and here's the project that uses it.
    |
    +- <UsingTask TaskName="BuildOrmLayerTask" AssemblyFile="$(TaskAssembly)" />

However, when project (2) builds, it locks onto the assembly from project (1). So now I can't build project (1) again without closing the solution and re-opening it.

Is there any way I can organize things so that the custom build task is not kept locked by Visual Studio?