We did this in a round-about way, by customizing the In-Store Pickup module, as this module can easily be duplicated. We have one instance of the module for each shipping method, and changed the word "hours" in the estimated processing time function to "business days", so it reads for example:

UPS Ground (Please allow 5-7 business days): $5
UPS 2nd Day (Please allow 2-3 business days): $12

so on and so forth.

Does anyone have an easier way to do this?