Missing Values As Non-zero

I am facing a problem importing Excel data into a finicky graphics program. This program can't accept strings and numbers in the same column. Hence, strings such as #NA, or Excel's standard "" can't be used where there are missing values, as the entire column is then ignored.

But, I would like to provision for future data below the rows that currently exist.

Let's say I am trying to read data from Sheet1 of a workbook. The rows in Sheet1 contain formulas referencing other sheets (e.g. Sheet2!C1-Sheet2!C2). So, if Sheet2 doesn't have data in a certain row, Excel would show 0 in the formula on Sheet1. That would mess up my graph. If I use any other string or "" using a If statement for missing data, then the graphics program doesn't work.

Is there any way say, using dynamic ranges or similar, to populate blank cells in Sheet1 as data arrive in Sheet2, without a pre-existing formula being present in these Sheet1 cells? I can imagine that VBA macros will easily do this (e.g. the thread on Autofill below). But, is this possible without having to trigger a macro as and when additional data arrive?