Currently there is no way to specify parameters from Gradle: http://testng.org/doc/documentation-main.html#parameters
Citing the link you gave:
There are two ways to set these parameters: with testng.xml or programmatically [in the test code].
Are you saying that one of these isn’t working?
I am requesting a feature to be able to specify these parameters in the Gradle DSL, in the same way that we can specify test groups (I would assume that it would involve adding a property to TestNGOptions and hooking it to the code that creates the test configuration)