How to reuse mock objects in Perl unit tests?

I have a bunch of unit tests for my module, and I find that I copy the same mock and setup code from one to the other. How can I DRY that up and reuse the mock code?

I've placed this simple mock object next to my tests:

package MockObject;
1;

If I just say use MockObject; in the test case, make test cannot find MockObject. Makes sense; after all, it's not installed system wide and it's not next to the module under test.

I can run my tests with prove -I lib -I t t/*.t but I'd like to keep make test, if only for the laziness of typing a few characters less.

Since the mock object isn't a full module and shouldn't be officially installed anyway, I cannot and don't want to set TEST_REQUIRES in Makefile.PL.

Adding test => { FILES => 't/*.t', INC => 't/' } to Makefile.PL didn't help.

How can I (simply) reuse Perl mock code with the MakeMaker generated Makefile?