Hi,
I found a really easy way to do this without creating an additional script.
#1: In LMP create a 'new list' called "Customers"
#2: Under "Additional Operations" when setting up the new list make sure you check the box that says "When users are added to this list remove them from the following list(s): " - then enter the 'list#' you want them removed from in the box.
#3: After saving your new list "Customers" just bulk upload your new customers emails and other fields using the "Import Users function"
#4: After uploading the email addresses, names, etc... they will be automatically removed from your 'prospects' list in bulk!
I've used it and it works for me...
Hope that helps,
-Dave
thinkandsucceed.com