For those who were entitled to EI before March 15, there is no problem. If they were entitled to these programs, they can continue to receive additional amounts from employers who laid them off, generally on a temporary basis. So, yes, that is an option. For those who have been receiving the CERB after March 15, that's not a direct option, as it is for those receiving EI benefits. There is not as much flexibility.
The fact remains that, if they wish, employers who have temporarily laid off some of their employees, who are now receiving the CERB, are entitled to increase it by up to $1,000. That increase is allowed under this program. Those employers can offer up to an additional $1,000 directly to employees; that's the amount allowed to date.
As I was saying earlier, the government continues to examine on a regular basis the possibility of adjusting all these programs. This includes the cases you mentioned in your question.