Ability to edit full copyright line, not just the name

I have no use for a copyright line, but I really want to display a little unobtrusive "Powered by [link]Drupal[/link]" line where the copyright line is located in this theme. There's a setting for editing the name of the copyright holder, however it's unnecessarily narrow in that it doesn't allow me to change the "Copyright (c) [year]" part.

I think the setting would be more useful if it covered the whole line instead.

P.S.: The spelling really is "copyright", as in who's got the rights to copy the contents. The incorrect spelling "copywrite" could be corrected in user-visible strings as well and if the variable is repurposed in an update to fit the whole line, maybe it can be renamed to the correct spelling as well - in fact, you could have an easy migration path by defaulting a 'copyright' variable to the following expression:

t('Copyright !c !year, !name', array('!c' => '©', '!year' => date('Y'), '!name' => theme_get_setting('copywrite_holder')))

but using theme_get_setting('copyright') instead if it's not empty.