New FCL
Flying_Hog, I'm in the same situation : Flying CJ2 and CJ3 under AOC so in a multicrew operation wit a frozen ATPL.
I never heard any CAA that let the ATPL test on a SP aircraft even if it has a MTOW above 5.7t. But the question was, is your flying hours on a multi crew environment are eligible for the 500 hours necessary to pass the ATPL. Those days, some CAA accept any flying hours in a multi crew operation and some only on a multicrew aircraft.
But the new Part FCL from EASA that will come next year is very clear :
FCL.510.A (b) Experience. Applicants for an ATPL(A) shall have completed a minimum of 1 500 hours of flight time in aeroplanes, including at least:
(1) 500 hours in multi-pilot operations on aeroplanes;
(2) (i) 500 hours as PIC under supervision; or
(ii) 250 hours as PIC; or
(iii) 250 hours, including at least 70 hours as PIC, and the remaining as PIC under supervision;
(3) 200 hours of cross-country flight time of which at least 100 hours shall be as PIC or as PIC under supervision;
(4) 75 hours of instrument time of which not more than 30 hours may be instrument ground time; and
(5) 100 hours of night flight as PIC or co-pilot.
But unfortunately, it is also very clear for the test :
FCL.520.A ATPL(A) — Skill test
Applicants for an ATPL(A) shall pass a skill test in accordance with Appendix 9 to this Part to demonstrate the ability to perform, as PIC of a multi-pilot aeroplane under IFR, the relevant procedures and manoeuvres with the competency appropriate to the privileges granted.
The skill test shall be taken in the aeroplane or an adequately qualified FFS representing the same type.
So as soon as you have a multi pilot aeroplane type rating, you can have the test as your hours on the CJ will satisfy the required experience.
Hope this help