Hello Charles,
The answer to your questions would be yes and yes. In theory, you can pretty much program the Keyfob(CC2540) to do just about anything. When the Keyfob bonds with Dongle A you can exchange a long term key (see section 4.5.2 of http://www.ti.com/lit/ug/swru270c/swru270c.pdf) that is stored in memory of the Keyfob. When a connection is lost and then restablished, this key can be used.
The other option would be to change the last 4 digits of the advertise information of the keyfob after its first connection and then have the Dongle A look for this info during the next connection. There are several other ways, you can choose the one that best suits you.
You can use the GAP Bond Manager Callbacks to customize your pairing routine and the GAPROLE for your advertising routine.
These are just suggestions and by no means the only way to do it. Nor will I provide any supporting code. You will have to familiarize yourself with the example code, the ATT, GAP and GATT by referencing the Bluetooth v4.0 specs from Bluetooth.org
Thanks,