I'm sure this would be possible, creating a token to store the value of Y and increment it for each text box. You'd need some sort of loop (i.e. For Each Value) to apply the text boxes but I'm not sure exactly what the use case is behind this. 

I managed to achieve something along those lines using a multi value field which starts with Y = 0 and increments it by a factor of 100 for each iteration (i.e. 0, 100, 200, 300). You'd need to experiment with the exact factor to make it line up.

I'm sure there are better ways, that's just one I played around with first. The token editor exposes the current value of Y for the text box as a token ("Annotation_Y") so there may be some scope there too.