A simple "conversion" from any licence to the FAA-licence is not possible-you will always (only) end up with a FAA PPL(H), and then have to show proof of completion of the necessary hours for CPL(H), ATPL(H) and/or IR (IR only necessary if youŽre going for the ATPL).
What i would recommend:
Fill out the form for conversion of your CPL(H) into the FAA PPL(H) (although it is not necessary, but at least it gives you another licence).
Then go to the US (you HAVE to take the exam there..), and find yourself a small flight school that guides you through the conversion process.
Check if you fulfill the requirements:
CFR 14+49 FAR/AIM text section 61.151 though 61.169 with special emphasis on 61.161.
FAA Regulations
At least youŽll have to do two checkrides (it is possible to do the IR in a Schweizer...donŽt know about the ATPL-checkride)...