There should be a checkbox, when building from a workspace, to restore the checkout to its pristine state.

I know you can do this with a build definition, but I cannot use build definitions[1] in my case and have to use workspaces.

For example, the git scm plugin has this checkbox.

See https://jazz.net/forum/questions/141370/scm-how-to-restore-a-workspace-to-pristine

[1] I can't use build definitions because I cannot create, update, and destroy them in a programatic fashion. Manually creating 100s of build definitions is too boring.