[MxxCon]

ok, you are confusing a few things here...
you got dynamic dns service account so your ip will always resolve to same "static name" as you put it.

when you connect to ftp you ALWAYS use ip address, not "dns name" as you put it.

what you need to do is get dynamic dns service account so you'll have dynamic host name that will always resolve to your ip..and it seems like you already done that.
now what you need to do is tell site administrator so use that dynamic dns host name to check for your ip, so server will automaticly resolve that host name and get your correct ip.
on the client side you need small software that will update dynamic host name with your current dynamic ip.

you don't need to make any changes to flashfxp