Set a fix rate for groups

How do I set a fix rate for group registration? So far, what I have done is use the individual registration to be able to set a fix registration fee for groups, but the limitation of this is that I can not get the information of each of the group members. What I need is to be able to set a fix cost for group registration, which is similar to Group Registration Rates settings, but uses Rate per Group rather than Rate per Person.