Extend code of 'multiple' widget: when 'Number of values' = 1 chosen: 'You have added 0 out of x allowed nodes.'

The main difference between single and multiple widgets is if the node i'm adding is going to be inline or I can add it with an 'add node' button.

Once I'd like to add a node also with a button (not inline) 'multiple' widget seems to be a good solution for me. Also in my scenarion it's obvious that only one node can be added.

A flag (with 'Hide 'You have added 0 out of x allowed nodes.' text') can solve this issue.

I'm thinking if there's any other module that would do this for me. Also i'm trying to use as less modules as possible and I want consistent, simple UI. Maybe some form alter hook would do it also for me?