I think they already have a hybrid Elance/Monster site to perform this- Elance. Once you have a rapport established with a contractor, there's nothing keeping you from sending them a job offer.
The vast majority of employers want to hire employees to work in their office. Elance is generally not designed around this goal.
I think a site like I'm imagining might restrict candidates to your local area and require that they be willing to work full-time and on-site. Maybe those would be optional, but that's the idea.
Elance does divulge where these people live- you can restrict your hiring/contracting patterns accordingly.
Similarly, if you are up for reloing candidates, you're not restricted to a local hiring area.
Also, you can make your wants and needs transparent up front. If a freelancer doesn't like the idea of working in your office for a salary, they're free to be honest about it before you hire them for the contract.
I think it's kinda silly to imagine a site that's a crippled version of what's already out there when the existing solutions are more than capable of sufficing in this limited case.
I think a site like I'm imagining might restrict candidates to your local area and require that they be willing to work full-time and on-site. Maybe those would be optional, but that's the idea.