Probably not, I'm afraid. What you're asking for is definitely against the rules, both in terms of general etiquette and CX policy as well.

However, rules occasionally get fudged. Here are my experiences with your situation, out of perhaps 35-50 F flights on CX:

1.) Split pax allowed to sit together for deplaning. For example, parents in F child in J. During 20 minute landing sequence, child allowed into F to sit in empty seat. Family deplanes together. In this situation the ISM came around and specifically asked the other F pax if they were okay with it. Seen a variation on this 2-3x.

2.) Split pax, one in F and one in back (not sure if J or Y). Two males. Guy in back was allowed to come up and play cards with guy in F for about an hour during the flight. He was not allowed to eat or drink. He left after an hour and that was it. Seen this 1x.

3.) Split pax, two males, wanted to swap seats midflight. Not allowed. ISM told them any seat swapping would have to be done pre-flight, and once the plane pushed back the assignments were final and visits would have to be done in the J or Y cabin. Would not permit anyone else in F cabin. Seen this situation 2-3x.

4.) Split pax: 2 parents in F, 1 infant (lap ticket, not sure if J or F), 2 maids in J. Parents were some HK celebrities apparently. Maids were allowed to come up and help parents in F for virtually entire flight (was Japan to HKG). This was a nuisance. Seen 1x.

5.) People try to come up to F, either to see friends or use lavatories. Passengers are escorted back quickly. Seen this many, many times.

Overall, this is definitely not okay. Although I've seen exceptions (described above), had the situation in #4 not been just a 3.5 hour flight, for sure I would've said something. And there was another Chinese couple in the cabin who were also visibly incensed at the situation.

Which route were you flying? Unfortunate, indeed. I've occasionally seen that happen, but overall this is the exception, not the norm.