create custom price response marketpress

I have seen references to this but no resolution.

How can I have some items in MarketPress 'email me for pricing'? Many of us sell standard and custom offerings that price has to be customized. Giving us the option that all the other eCommerce plugin carts provide to say---

Product- On-Site Training Course=== 'mailto: contact@domain.com subject: pricing for course. Or pass an html link to our contact forms.

thanks

Mike