So what I understand is that you would like device a) to be the peripheral device b) to the central which is also connected to device c). You would like the code to send signal/indication/notify from b to c when a meets a certain standard?
This sounds similar to UART example, except now your working as the central. If you are using a nordic chip as your BLE, I would recommend looking at their SDK v8.1 in the S130 Soft Devices Folder specific to the Multi-Linking Heart Rate Monitor(HRM) example. Essentially what I recall is that you have to invoke a second instance of the BLE in order to have a separated Server Client, but simpler than this would be to use the server side notify option in a schema similar to a cell phone notifying a watch. It sets the standard to allow the client to push a notify to the server.
These are my inexperienced understanding
@JPaul: I haven't looked at your logs very carefully, but it seems you've made progress with your project.
Regarding sharing code: you could send me a link to an unlisted repository (under your account) on mbed.org; my user-id is rgrover1.