How can we increase a project funding without creating a new budget?

When closing projects where a small funding increase is required, we have always used a procedure part of which involves ticking the Baselined Funding Without Budget checkbox under Billing Set Up. 

 

Now, when we tried to do this in order to process a 4.00 funding change on a project, we get a message that states this field is protected against update. 

Apparently this was a BUG & according to Oracle Support, this wasn't supposed to be allowed, so.., here we are, how can we achieve the same result without using this checkbox?

any ideas? workarounds?

Thanks!