Actually, you need to research the use of URI rules. See REST Data Protocol Handler - DevTest Solutions - 10.1 - CA Technologies Documentation
In the above, your URI rule would parameterize the car make and form a rule allowing it to pass into the VSI.
POST /tst/cars/HONDA/test
POST /tst/cars/TOYOTA/test
POST /tst/cars/BMW/test
Would contain a URI Rule parameterizing the make into POST /tst/cars/{URLPARAM0}/test. This would be the operation in the VSI. Each specific transaction (HONDA, TOYOTA, and BMW) will show up as specific transactions under the POST /tst/cars/{URLPARAM0}/test operation. The value of the car make will be in an argument called URLPARAM0.