I have N:N relationship between account and custom address entities. On account form, I have subgrid for custom address. how to open create form on click of subgrid + button? currently, it shows look up search behavior.

I have N:N relaationship between account and custom address entities and on account form, I have subgrid for custom address. On click of subgrid + button, it shows look up search . But I need to change that to show create form pop up. I know in this scenario , I should have used 1:N relationship between account and custom address but at this point, I cannot change that. I tried hiding "add existing associated" button on ribbon but that was hiding + button itself. I want to subgrid + button but want to open create form on its click event. Any help or pointers would be very helpful.