JAR-FCL 2.240 (a) (4):
The holder of an IR(H) valid for a
single-engine helicopter type wishing to extend
for the first time the IR(H) to a multi-engine
helicopter type shall satisfactorily complete a
course comprising at least 5 hours dual
instrument instruction time of which three hours
may be in FS or FTD 2/3 or FNPT II/III, plus a
multi engine skill test in accordance with
Section 5 of Appendix 2 or 3 to JAR-FCL 2.240
on that type, at an approved FTO/TRTO.]
Hope this helps.
Peroo