We don’t have such an option as in the link you showed to me for the dsIDXpress compatibility. I’m not sure if you’re asking about dsIDXpress, or a search for MLS in general.
In your link, the search came with the theme? Or the search option was created by your MLS?
Maybe the plugin has a similar search option which you can use with the plugin, once activated, and we just have to create CSS for the position of the search? It’s just an idea, I don’t know if it’s possible. Each IDX plugin is different.