Can a CRM 3.0 PreCreate callout fill form fields in advance?

I just开发者_JAVA百科 finished my first CRM callout, and it's working great, but it doesn't actually seem to take effect until the form that calls it is saved. It's a PreCreate deal that assigns a value to one of the attributes present on the form. Is there any way to get it to assign the new value and display it on the form as soon as you load it, or is this just the way it works?

You'd have to add some JavaScript to the onload event of the form and default any form fields that way. Callouts don't fire until after the save event happens, so they can't be used to default fields in the UI.