After 1500 hours and an ATPL check ride, your MPL will still be an MPL but think of it as an MP-ATPL. You can't legally fly anything bigger than a 70kg trike on your own, other than in the capacity of student pilot perhaps, so they aren't likely to let you loose teaching on that.
Talk to the authority and see if they will accept PICUS towards either the CPL requirements or the 150 hours PPL/FI - it's really down to their interpretation. Otherwise, bite the bullet and get yourself some SEP/TMG hours. If you're looking to get more hours to upgrade then it'll pay for itself and cost you nothing.