If you are an FI then why are you doing the CRI course?
Would it not be better to have the limitation on your licence restricting you to instructing on single engine aircraft removed?
To have that limitation removed you have to meet the requirements of JAR-FCL 1.380 (a)
The 10 hours in the last 12 months you refer to are only applicable to CRI's who want to extend their privileges to another class or Type.