From a theoric point of view the answer is yes, but the actual implementation is not straighforward.
You must manage the remote update core and the epcs with HDL code.
IMHO the best approach would be to implement a simple microprocessor in HDL (if you don't want to write your own, you'll find something on
opercores.org) and use it as you would do with Nios.
Using uart is generally easier (let's say less difficult) since you have simpler driver and communication protocol.
