Hader Clip Techniques?

Dr. Robbins asks:

I am having some problems getting a mandibular overdenture to fit the bar. The patient has 4 dental implants supporting a bar in his mandibular anterior region. I cannot get the Hader clips to seat on the bar.

I have picked up the transfer copings off the bar in an impression in
the overdenture and given it to my lab. The lab says the most accurate
way of mounting the Hader clips is to pick up the Hader clip in the
overdenture using acrylic. I am a little leary of locking the acrylic
under the bar.
Does anybody have a good and reliable technique for this?