We ran into this problem a while ago and found that it was quite a bit of overhead to set up workflow manager service for a dba to request if that is the only person that will use it. It is possible to run a geoprossessing service from a URL especially if they do not have any parameters.. It just takes a little research into the submitting requests using the REST API.
Yes, using the REST API is certainly a preferred option because of cross platform usability. I would suggest exploring the viewers available on the workflow manager resource center to see how these things are done.
There is video here showing how to use our JavaScript API in creating jobs via a standalone website - http://video.esri.com/watch/3263/getting-started-with-the-workflow-manager-web-apis