Excel: Leave a cell blank if condition is false

Other questions have touched on this and offered solutions that are not viable for a very large data set. . . I have a formula like the following:

=IF(A1=A2, B2, "zz") across 9 columns

I then autofill about 3.5 million cells + copy -> paste values. Then I find and replace "zz" with 'empty cell'. However, finding and replacing a million or so 'zz' strings is a very slow process. I'd rather not write anything there in the first place. So my question is, how to I write the following formula:

=IF(A1=A2, B2, 'leave cell alone and write nothing there at all')

Excel seems to be incapable of not touching a cell in case of FALSE (or TRUE for that matter). Can this be done?

Thank you for your insight!