Remote Support w/ Unattended Access Option

I am looking for a program that will allow me to access clients remotely and without interaction from them, such as the ID and password requirement in Teamviewer. We currently use Dameware MRC but with our growing customer base it is becoming less cost effective to continue using it since we have to install and license a copy on each domain we want to use it on. Teamviewer seems to be a good option but the need to have the client give us ID and passwords, even once, is cumbersome and not an ideal setup. With the number of machines we service and the limited availability of the end user (most of them are in the medical field) even the initial setup of Teamviewer could be an issue.

That being said, I have only used the free version of Teamviewer, never the corporate. I have been doing some research and saw that there is an option to make your own Teamviewer servers? When doing that does it allow me to assign IDs to end users or are they still randomly generated? There is no free trial of the corporate version so I'm unable to try this out on my own.

The problem with Dameware is that it is more for a company's IT department then it is for an IT company with numerous customers. I have been trying out the Dameware Remote Support product and it requires that the machine it is on be a part of the domains being worked on (at least as far as I can tell), which is not something that can be done easily.

I need something that will allow me to access multiple domains while also allowing me unattended access to the end user pc like Dameware MRC does. Is this product out on the market or are they all aimed for company specific IT departments? We are going to be making a decision on what product to go with and I am trying to get as much information together so we can go with what will work best and be cost effective. I would appreciate any suggestions greatly. Thanks