We have plans to support this scenario (or something close) in our next release (2011 R2). We are adding drag and drop sequencing for backlog items (similar to what we have currently for Bugs on the Assign screen). This sequence is user set and not driven off the current Priority field.
If this sort of sequencing works for you, perhaps then you could use the Priority field as your Business Value? I assume you want a numeric field for this? But if not, you could use the Value Classification drop down field as your Business Value.
The values available in the drop downs can be customized via XML by going to the Settings tab, click on View Settings then click on the small 'Advanced...' link located near the project template specification. Please use caution when editing these settings, and only edit them if you are comfortable editing XML.
If you need help, or have more questions feel free to ask.
the Telerik team