As you know FM can't send multiple attachments in an email (need a plug in for that) but you could export out each PDF fomr container fields (don't make them global fields or you can't upload to them in a hosted solution and have them saved) one at a time and append them to each other to make one multi-page PDF that you can attach to an email that is how I did it.
Your answer doesn't make sense to me, unless you are saying that you are "appending them to each other" using an application other than FileMaker. The FileMaker Save as pdf script step includes an append option, but it appears to operate on the whole record or layout, rather than a specific field or pdf files outside of FileMaker.
You're right I'm sorry. You can append records saved as PDF's to an existing PDF file you have stored in a a container filed but to combine multiple PDF's together to attach in an email you will need the PDF Manipulator plugin from PC found here: http://www.productivecomputing.com/pdf-integration. Sorry to confuse you!