We did that for several years with web apps over SAP.

We developed a series of reusable building blocks, grabbed from one implementation to the other. But what was presented to clients were nice and trendy png screens, based on the last information we got from them.

Leaving our competitors in the dust, with their product releases, documentation and aging interfaces.

But it's over now, today I'm in a SaaS startup, and here we can't fake anymore. When people try your app, they see the real thing.