I had the same issue with some Symbol barcode Scanners I am working with.
The scanners come with documentation and printed on that documentation are barcodes. I had one in particular that says "Carriage Return/Line Feed"
I scanned that barcode and the scanner beeped and accepted the code. From that point forward it will scan the barcode, and then drop down to the next cell.
In Excel you can also tell it to move horizontal as opposed to vertical if you wish.
I assume every scanner has this type of instruction sheet or documentation... so just look up the model of scanner you have, go to their site, download the documentation and it SHOULD have those barcodes that you will need to make teh scanner do what you want it to do, or emulate what you want it to emulate.
The scanners I have , have NO buttons etc on them, and are wireless USB scanners, and that is the ONLY way I found to make it go from one cell to the next either vertically or horizontally.
Mike