Hello Bella'sMom -
There is an option in your account preferences to have the optional eBay gallery images added to your listings by default, which has been available for quite some time. After logging in to your account just select "Acct. Preferences" from the My Account menu and this is the second option from the top of the page. It is in the Listing Management section and there is a checkbox labeled "Enable the optional eBay gallery by default:" as noted here.
Please also note that not checking the box for the Optional eBay Gallery images does not prevent images from displaying in the body of your listing as this option only affects the gallery images that display beneath your Header image on eBay.