Talk to Dave and see what he has to say.
He's a good guy.
I am guessing that the install only is for one of tow reasons
1. Shipping
2. Liability
As for #1, I think people have picked up the clips at his place before, but maybe he has changed that.
As for #2, maybe he is protecting himself in case people say there is something wrong with them.
I am honestly guessing ... talk to Dave, tell him I sent you and see what he says
The price of shipping the clip from him to you might be more $$ than having him install it.