I don't think there is a solution around this. The Excel Write step could be setup to to handle replication number, but you would only be able to run one replication at a time. The same worksheet cannot be opened more than once. The way the Excel Write setup works, it opens the worksheet into memory, writes the data into memory during the replication and saves the worksheet when the replication completes.
I recommend using the DB Write step and a MySQL database. MySQL is easy to setup and free to use. We provide instructions on how to setup it up in the DBReadWrite simbit. With the DBWrite, multiple replications can write to the database simultaneously and all the replication can be written to the same table. Once the experiment completes, you can import the data from the database into excel. In the end, the DB is the quickest way to get all your experiment results into one place.