How to pass parameters pickled and not netref in rpyc callback

Question

Hi I have a scenario where i have an RPYC classic server and a callback registered to some operation. Parameters that are passed back on the callback are protobuf messages. (This is my system and i cannot change it). Now i noticed that callback is very slow, (can take couple of seconds) and i have a significant rate of those callbacks I tried to manually "pickle" the parameter and unpickle it on the "client" side (the side that registers) callback. This yield significant improvement over netrefs (X10). The only problem is that it makes callbacks complicated, as inside a callback i have to manually pickle (on server) /unpickle (on client). So the question is whether there is any way to force RPYC to pass parameters as pickled (As it was in older RPYC versions) or at least for this specific callback. P.S. i dont care about security in this particular case as this is a "mock" testing system.