L10n of numbers?

I need to localize numbers in text fields and have been looking at the
various L10n plugins that claim to have number support. Support seems
to mean that the plugin includes a Number#to_localized_string method,
which isn't very useful for my purposes.

I figure I could build my own numeric_field helper easy enough; the
question is how I'd go about parsing the input before it reaches

Currently I'm thinking along the lines of prefixing the field names
with some string, e.g. 'numeric_value_', parsing the (possibly nested)
parameter hash (from a before filter?) looking for these things, and
then adding them back into params as standard English-formatted
numbers without the prefix.