Only way with a locked Bootloader is described here:
But it is still in development and I would not advise it if you're not 100% sure what you're doing.
You could also unlock your phone and flash the Advanced Stock, Doom or any other kernel containing a recovery, but you will loose your Sony DRM Keys (Camera, X-Reality,...). They can be backed up (Backup TA partition) and restored, but the procedure is not that easy either.
Is this banking app really that important?