[jQuery] building a custom "speed"

[jQuery] building a custom "speed"


I was wondering if any one could point me in the right direction for
creating a custom "speed" plugin that extends the current speeds. For
example right now I use slideUp('slow'); . But I want to use
something like slideUp('custom'); . Where "custom" takes the height
of the object and computes the number of ms to return for slideUp.
ie
slideUp( (($(this).height / 470) * 1000) );
but I would like to write it like ...
slideUp('custom');
Thank You