Question: What sort of keyboard parts are you looking at adding?
Reason I ask is I wonder if you could 'fake' them with other techniques, or get other band members to play those parts on their instruments. Brass lines often translate well to guitar for example.
Or with a bit of two hand tapping you could play a simple melody with the right hand and tap out a simple bass line with the left. For example, the opening to 'Paradise City', I hold down the bass notes and play the brass notes with my right hand at the same time. Or again, I play the piano intro to 'Mamma Mia' with tapping a la Stu Hamm's 'Country Music' style.
Although if you can do this, you could just as easily play keyboard with both hands
However if you are dead set on playing keyboards and bass yourself, I really, really do think you'd be digging a hole for yourself by attempting to cover the bass with pedals. Getting two hand coordinated is difficult enough, getting hands and feet coordinated is another level. Even accomplished keyboard players find it difficult. I really so advise to work on your left keyboard hand. You never know, it might improve your bass technique too.
I think your other idea of getting an actual keyboard player is better though!
