CX's own Ruby members (Silvers) get priority baggage on CX. However, my understanding of how it works, esp ex-HKG, is that the "priority" is coded into the bag tag barcode, i.e. the blue/red "priority" tag is more of a flashy indicator than an actual means for baggage handlers to identify priority vs. non-priority bags. Since your friend is on a different flight altogether, he/she will not get the same priority barcode as you. You may be able to get the agent to apply a tag to his bag, but I wouldn't expect it to deliver any real benefit.