scripting: bottling spontaneity

I'm having a very challenging time with a project I've been working on, and I'd like to ask for your advice.

Here's the challenge: when I need to speak in public I have no problem being spontaneous, I can work from some sketchy note cards or outline and produce something that I and my audience find satisfying.

But when I need to sit down and write it all down first, it doesn't fall out of my head at either the same rate or quality that I enjoy when I just stand up and do it.

Have any of you ever "recorded" yourself then transcribed it as the foundation for a speech or other creative project? Did it work?

Thanks.