Shared access. Grant access only to specific envelopes

hi there. i got a client who has this need. to grant access to only specific envelopes. Shared access grants access to all. if there was a way to grant access only to specific envelopes and not to all, it will be helpful..

This is the case when someone goes on holiday or unavailable and need coverage on the in progress and completed envelopes for a period of time but needs privacy over other envelopes in his/her inbox…

Thanks