Is it something vocalists (generally speaking) can have problems with?
In my experience, they are usually capable of learning it.
You might try to use this problem creatively, eg. say the last chorus chord is C and first verse chord is B. If the singer sings A (6th) as the last chorus tone, he can still keep the same tone on beginning of the verse, where it changes to flat 7th. You get change of mood while keeping the same tone. This will work with another tones similarly (3rd going to 4th, 1st (C) going to flat 9th, 5th going to flat 6th etc.) and way more interesting options appear when you start thinking about two tones in a melody. With overlaps like this, be it voice or instruments, you can perhaps avoid the cliche of going a step down, which might be felt by the audience as dropping the power.
