Try Barcodescanner Keyboard. It seems to do what you want.
Soft-keyboard with integrated camera bar-code scanner lets you scan wherever you can type (free demo). This soft-keyboard scans and enters barcodes directly into input fields of arbitrary apps, batch scanning mode is supported. It reduces manual typing and eliminates copy and paste. A special key invokes the built-in or an external camera barcode scanner. The setup wizard makes it easy to install the app.