If you know the length of the response, 12 in this case:
Code:
HSERIN2 1000,SYNC,[COM\12]
Since the normal response packet (except image data) seems to be 6 bytes and the camera response to a SYNC is an ACK (6 bytes) and a SYNC (6 bytes) I'd probably do it in two steps
Code:
COM1 VAR BYTE[6]
COM2 VAR BYTE[6]
HSERIN2 1000,SYNC,[COM1\6]
HSERIN2 1000,SYNC,[COM2\6]