you can do something like:
slots:
foobar:
interface: serial-port
usb-vendor: 0xabcd
usb-product: 0x1234
usb-interface-number: 0
path: /dev/serial-port-myserial
if you know the vendor and product ID’s if the to be attached device. After you connect the interface your application can then talk to it on /dev/serial-port-myserial which the interface creates for you …
(i think there was also an option to use serial numbers in the above block, to make the setup even closer bound to a particular device)