I've found a few posts were people have posted this same issue - but no resolution has been given yet. The issue is hard to explain so I'll take a shot at it.
Call Manager Express 4.1 - Shared line appearance issue.
Let's say there's a shared line on my Assistant and Executive phone. This shared line is setup as a 'dual-line' and can handle two calls. When a call rings in the shared line rings on both of the phones as expected - Let's say the Executive phone answers this first call. The issue appears when a second call comes in and the first call is still in progress. This second call is then delivered to the Executive phone and the executive has the option to take the call but there is NO indication that a second call is ringing in on the Assistants phone.
Does anyone have a solution for this issue? My only other option is to make the Executive line a single-line and call forward busy to a backup executive line that is another shared line appearance on both the Assistant and Executive phones.
never configure ephone-dn as a single line because you will be unable to do consultive call transfers and ad-hoc conferencing with it. Use "huntstop channel" instead.
To have a shared line present further calls to all phones, the only solution is to configured call forward buys to another extension. This extension is usually configured in overlay with call-waiting (c separator) on the same button.
I have never figured this one out, but this is the actual design;
Shared Dual Lines
The Cisco Unified CME call-handling model allows only the active ephone of shared dual line DN to receive additional calls. That is, if an ephone is active on a call on a shared DN, other ephones with the same DN will see the DN in use. If a second call is made to the dual-line DN, that call is only presented to the active ephone. The other ephone does not receive any indication of the second call.
I think your plan "B" is the way to go!
Sorry man but I hope this helps a little,