I would think you would want to add a new drop-down on the TechnicianIncidentForm rather than add them to the groups drop-down. You could do a bunch of things here, either add a new list and include all the people you want to include and then add an assignments piece to the workflow so that the selected user would also be added to the assignments list, which would be all static, or you could try to get fancy by selecting a group and then have the form reload populating the user assignment list with the members of the selected group. Then you would add an assignment component to the workflow as mentioned previously so that you can assign the incident.
A bit complex sounding but it shouldn't be that hard. I too am on 7.5 so troubleshooting will be a bit difficult but can try to help when I can.