zip code radius proximity search on Portal

From a brand Rollbaser: Does anyone know how to do zip code radius proximity searching on a Portal page? I have an Object definition with the Location attribute, and can do "Search by Distance" as a Rollbase admin. I also know how to create a View and then add/config a Search form in a Portal. However, there is no My need is to execute a "Within ___ miles from US Zip code _____" on a public Portal page. Thanks for your help/time.