Calling a form with some fields populated

It would be nice to be able to call a form e.g. a contact form with the description / subject field populated depending which post called it.

e.g. I want to have a ‘any questions’ link on the bottom of each post and that will display the contact us form. I would then like the post to call the form e.g. [sform]2[/sform] and with Subject= ‘Question for car tax post’.