You could do this through a workaround right now, in combination with Dblue’s pattern length from sample tool ( New Tool (2.7): Set Pattern Length From Sample -> only works with 2.7.2 I think)
make a selection in the pattern through mouse click and hold (for the length you called ‘block’), right mouse click, go into the ‘selection’ menu and choose render to sample. Doesn’t matter if there are note events/sounds triggered in this selection, it is a bout the length of the rendered sample.
Now run the tool and make sure you have the rendered instrument selected.
edit: lol