414(s) and preparticipation compensation

[LIBERTYKID]

Plan permits a participant to make salary deferral contributions immediately after hire but may only receive an employer discretionary contribution after a year of service based on compensated earned after being eligible for the employer discretionary contribution. Assume a person is hired on April 1, 2014, and is first eligible to receive the discretionary contribution on and after April 1, 2015. In testing the compensation used for the employer discretionary contribution for discrimination under 414(s), do I use the person's total compensation from January 1, 2015 or April 1, 2015?

I understand that pre-participation compensation can be excluded, but can I treat eligibility for the discretionary contribution separately, or does the fact that the employee was eligible to make salary deferrals for all of 2015 prevent me from doing so?