I'm not sure if there is already a way to perform this task in Wave Editor. But if not, I have a request that it'd be possible to make a selection within the audio file, and then, in order to easily set the grid lines according to the length of what you selected, I wished there was a function for that in the menu.

This feature comes in very handy, especially when editing rhythmical material, where you want to quickly conform asynchronous beats to a grid, which was made out of any chosen beat that you've first selected.