Is it possible to create views pages with urls like "prefix-%-postfix" instead of "prefix/%/postfix"?
No. The menu router system only understands
% as placeholder within
/ characters as an argument to pass through to the callback function that will render it. It won't understand
prefix-%-postfix other than its literal value. The underlying function,
arg(), that the Views
Content ID from URL contextual filter relies on to retrieve an argument relies on this system so it wouldn't be able to pull the argument.