The Pro Options section within the Lightroom plugin's interface is a text area where Pro Options can be entered as text in the form optionValue="optionName" (e.g. autoPlayOnLoad="TRUE").
Please see the Alternative Methods to set Pro options section at the foot of the Lightroom plugin's support page.
None of the Juicebox plugins are as fully-featured as JuiceboxBuilder-Pro (which comes with Juicebox-Pro and has individual controls within its interface for all Pro Options) and they are provided as a convenience for users who already use programs such as Lightroom and want to be able to create Juicebox galleries within their existing workflow.
It is actually quite a quick and easy process to open a gallery (created by the Lightroom plugin) in JuiceboxBuilder-Pro, customize the gallery as required and re-save the gallery.
You could even create a preset in JuiceboxBuilder-Pro so that you can quickly apply a collection of configuration options to an existing gallery in a single action.