multiple versions of rss feeds?

is there a nice way of getting two versions of an rss feed?

the settings panel lets you nominate whether you want full text or summary.
but what if we would like both?

feed1 = titleonly
feed2 = full version

prefer not to modify core.

i’d guess at copying wp-includes/feed-rss.php to feed_rss3.php
and selecting my content inside there.
but then i’d probably forget to upgrade it in the future.

any plugins or template based ways of doing it?