I would really like this feature, too. I'm doing by using late fee after the early reg date, but I think it is confusing to the registrants to have it listed that way.
I also wish to have deposits and multiple payments, too, but hacking custom fields with late fees doesn't work very well.
Could you rephrase your event description to make your "regular fee" your "early bird fee" and your "late fee" your regular fee? This would give the illusion of an early fee without modification of the existing component.
For example, "Register before mm-dd-yyyy and receive our early bird rate of $5! After that, our regular rate of $10 applies." The downside here is that you will not be able to do a true late fee since you have already used it.
This is now possible as of DT Register 2.5.6 You can establish an Early Bird discount of $ or % and provide the deadline date for getting this discount applied.