The situation: Ok so I've got this song I'm writing, it's in A. The chords for the verse are F#m, D, A, E. The song is more complex than the chords let on, but that's not really the issue. Part of the melody I've written includes a section that, on what would be the 5, E, I play a B then hold on a Bb before returning to the F#.

The snag: Since the Bb is the major 3rd of the F#m "root" this would imply a key change (going from A to D).

My problem: This is what I want to avoid. I don't want a key change, I want to use that note, but still transition back to an F#m with the feeling of returning to the root. The way to do this is to create additional tension below with some random chord and I'm sure there's some really obvious aug or dim chord that I could use here, but I can't seem to stumble upon it myself. Anyone have any suggestions for incorporating this? I swear it happens all the time in flamenco music.