Web app items, accept payments through the app submit form.

Accept payments for web app items. It seems that forms can accept payments, web app item submit forms no. Use case would be to have site visitors submit ads (through a web app) make a payment, then the site user could approve the ad and make it live through the web app. Then we don't have to copy and paste into a new web app item that we have to create. I don't see this feature already.