Append measures on truncated paste
When pasting e.g. 16 measures of notes into the second last measure of the score, pop-up a modal dialog box:
There are not enough measures left in the score to paste this selection here, do you want to:
X] Paste what fits, keeping the score the same length.
X] Paste the whole selection, appending enough measures to the score to make it fit.
You could also add a checkbox "Don't answer this question again - always use this strategy."