I dont use the app, but I dont think the app necessarily requires you to have LX/LH accounts to check in to your LX/LH flights.
For sure you can check in through the LX/LH website, then elect to have your BP emailed to you. In the mail should be a barcode image for eBP, along with an option to download the .pkpass file if you want to open with boarding pass apps. (On my android phone, i'll hit the link that says to "Open in Wallet" even though Wallet is an iOS program...)