Using PayPal API signature

[Michael]

I'm setting up Potion Store for a client who is attempting to migrate
from a proprietary storefront. The old storefront will need to stay
operational during the switchover, but there's a catch. Potion Store
seems only to work with a PayPal API certificate, but his current
storefront requires a PayPal signature. PayPal accounts may be
accessed with either a signature or a certificate, but not both
simultaneously.

Has anyone successfully added API signature support to Potion Store? I
would attempt it myself, but since I'm new to both Ruby and the PayPal
API I'd likely end up digging myself into a hole.

Thanks,

Michael