Louis:
I actually wrote an article on this a while ago with a how-to (
link here)! I was having the same design challenge for our own landing pages.
The JavaScript there takes the "Instructions" field on each input field and makes a new HTML5 "placeholder" property for the input field. Then you throw in an HTML5 Placeholder shiv of your choosing (example included) so that it works for all browsers. I found this is the best way to do it for Marketo, for
all the reasons described in that article.
You can see an example of the final result on any of Yesler's landing pages (
this recent webinar one, for example).
Let me know what you think!
Best,
Edward UnthankSEO/Web Specialist
Yesler