I have always divided the annual (12 month) salary by 2080 (approximate work
hours per year)  to get an estimated hourly rate. I also footnote the budget
page with something like the following:

"Hourly rates are provided for proposal purposes only. Employees are
compensated on a percent-of-time basis. Employee effort is documented in
accordance with OMB Circular A-21."

Diana L. Hyde
Grants Specialist
Contracts and Grants
Florida State University
109 Herb Morgan Building
Innovation Park
Tallahassee, Florida 32306-3067
Phone: (904) 644-8676
Fax: (904) 644-1464