Very good post from B2N2.
No matter what anyone tells you, if you instruct in the USA in an N reg aircraft you are on very thin ice without a CFI certificate.
You most certainly cannot send anyone solo.
It's been debated for years, but bottom line in my opinion is if you wanna work in the USA as a flight instructor training JAA pilots, you better get JAA/FAA qualtified. Believe me you don't want to fall fowl of the FAA.
Regards