custom filter operater?

[James]

I'm trying to apply a filter on some data in a column that can't be compared in it's existing form using the existing filter operations. The data in the field being compared is a string representing a date, but it's received in a format that doesn't make comparing it directly work. So, for example, the date is in the format "2012-2-28". I need to compare it to another date (the current date, for example) but I would either need to have a custom operator that could compare date strings formatted in this fashion, or I would need to be able to pass the field's value to a function that converted it to a form (say milliseconds) that could then be compared to the value I pass in. Are either of these scenarios possible? And by compare, what I'm trying to do is find if the value is greater than or equal to the date value for the field.