Setting focus in a form and screenreaders

I've been asked to create a form and on page load have the focus set to 
a particular field in the form. I've used some javascript to do that.

It then occurred to me that a screenreader, on loading the page, would 
be immediately at the form filed and miss all the information before the 
field.

I tested briefly in a demo copy of JAWS and found that to be the case.

It seems to me this is a major accessibility issue for the form. Would 
an experienced screenreader user has some way of overriding this 
behaviour which would mitigate the problem? Are they any alternative 
ways of accomplishing the same thing?

Thanks for any help.

Mike