I'd like some help passing values via URL

I know i can add ?Fieldname=value to the end of the URL to pass a default value.

However, is it possible to do this to a subform?

I've tried ?Subform.Fieldname=value with no luck.

EDIT:

You can pass the value to a placeholder field in the main form, and have it copy across to the subform on load.

Still would like a direct solution, though.

Thanks, 

Levi