Creating A Web Popup For Selecting An Option

I am looking for some design "best practice" or heuristic to address performance issues on a webpage.Basically, there are dropdown menus with up to 10,000 choices and each is in an tag. So I have many thousands of extra nodes in the DOM model. I think this is slowing down the javascripts that parse the document after it loads, but also it is slowing down the initial page load to get out all that data.I would like to lift those drop downs off the page entirely, so instead of combobox style controls, it will have a link to a modal popup which will contain the picklist. I think preloading and caching these popups on the client will prevent the slowness of loading the initial page, and get all those 10,000s of off the DOM so that the existing script performance will improve.

With my limited experience in web development, I am not sure if the best thing is to create some sort of page/control/service/etc for the initial approach.Once I am confident I am using the correct approach, I should be able to work out the details.