Rotate a bone thru other two bones rotation?

[Genete]

For the 3D hand I'm developing I need to rotate a bone sometimes yes sometimes not and it depends in the rotation of other bone.
So, it is possible to have an embedded script that rotates a bone as a combination (linear combination) of other two bones? It wolud be fantastic for me and I supouse for other multiple users!!!.
I'm very afraid about the amount of bones that I have in my 3D rigged hand so the script should be smart to prevent full feed back of the rotation of the slave bone until the keyframe is released. I mean, during master bone manipulation the script should not send to the slave bone any information. Only when the user release the master bone (and the keyframe is modified) the script should calculate the new angle for the slave bone and create a keyframe for it. Perhaps we are talking about a script tool instead an embedded script.
I'm very close to have a reliable version of a 3D hand "with volume" so all the help in this area would give more usability to the 3D rigged hand. It would benefit to all AS users of this forum...

Thanks in advance to all the volunteer scripters in the forum and to anyone who contributes to this request.
Regards
Genete