British-style crypitc/quick puzzles, in which words are linked every alternate letter, have a regular pattern of blocks. You can quickly fill in the basic pattern by choosing Fill alternate blocks from the Grid menu.
Block filling fills in every alternate block on alternate rows. There are four choices of starting position - just select the button for the one you want.
Note that fill from (2,1) and (1,2) is not compatible with dual-symmetry.
You can also generate an entire new random pattern by using Generate Pattern.