I am currently running the latest Jenkins (1.457) and the latest of the scripttrigger plugin (0.16).
By simply selecting the "Poll SCM" checkbox (utilizing CVS plugin for SCM) in the configuration history I am able to see the "Poll Now" button on the main job page, however when deselecting "Poll SCM" and selecting the "[ScriptTrigger] - Poll with a shell or batch script" checkbox there is no "Poll Now"-like button to hit. That then requires manual tweaking of the configuration file to get the trigger to poll on demand by setting the schedule for a time within the next minute.
If the button can be added it would probably be best to have it called something along the lines of "Poll ScriptTrigger" since both "Poll SCM" and the scripttrigger polling checkboxes can be selected allowing for multiple "Poll Now" buttons on the main job page.
I'm not sure if that is the information that you wanted, so let me know if you need more.
If this seems to "out of the way" for very minor functionality, I'd be alright with closing this issue. However, it if it's fairly simple then it would be very nice to have (and cut time testing out my script .