Premiere Rush - how to purchase Preview videos after composing entire project?

I composed a project using Preview videos. I have edited them for length, added audio and titles etc, to get the project how I want it. Now I am ready to purchase the clips I used. Is my only choice to buy them through the Stock page and then start over with this project build, or is there a way to buy/license the Preview videos from within Rush, and have these videos on my project instantly update in-situ with the watermarks removed? This would save me tens of hours that would be needed to start from scratch. If a "license your preview videos" option is NOT available in Premiere Rush, is it a feature of the full version of Premiere instead (in which case I'll have to start using that instead of Rush)?