NUnit runner assembly selection - creates many nunit files instead of one

Using version 10.0.2 (build 42234) (will upgrade soon, promise). I would like to specify assemblies for an nunit runner step like so:

**\bin\Release\*UnitTests.dll

When I do that, TeamCity finds all the relevant files, and then creates a .nunit project file for each one (presumably, this is one for each folder or something?) and then it runs a new instance of nunit for each .nunit project file it has created.

If I change the build configuration so that before this nunit step I move all the files that match my pattern above to a single folder, and also adjust my nunit step to use pattern like

%unitTestsFolder%\*UnitTests.dll

Then TeamCity creates a single .nunit file and runs one instance of nunit console, and then I can use parallelisation command line args etc to make it faster.

I want to use the former style because different unit tests may reference different versions of the same assembly and so cannot be placed in a single folder without conflicting. The question is, in the first configuration can I force team city to create one .nunit project file? Have I misconfigured TeamCity? Or do I have to roll my own test-runner step? (easily done, but non-ideal)