You can’t price a trip AGP-LON via some out of the way place and pay the same as you’d pay nonstop because it’s not in the BA routing rules. Not sure if they let you fly AGP-MAD-LON on IB for the same price but that doesn’t bump the TP that much. But you could construct an itinerary using two separate one-way Finnair tickets, like:

AGP-HEL-OSL (AY business lite) 140+40TP
OSL-HEL-LHR (AY business lite) 40+80TP