White board
n.

A thing or (preferably) person upon which a writer throws all his/her ridiculous ideas so as to open up mental and creative space for the ingenious ideas to flow in.

Writing the final scenes was a headache but once Esther came in as my white board I was able to figure out the ending.

v.
White-boarding

To serve as a white board for someone, typically a writer.

I love white-boarding for John whenever he starts writing new work.