Not sure if that's possible with the native people app, but I downloaded a free speed dial app, loaded it with the contacts I wanted immediate access to, and put out a shortcut to it.
To make it clearer, when you add a contact, you want it to default to a group or do you want to be able to see a specific group when you click the people app?
I haven't found it, but I use Folder Organizer and that you create a label say Friends, and you go in the contact part of FO and add the label to the contact. Then create a shortcut to the folder item called Friends.
Sent from someplace, and with something that you need not worry about.