I see there's availability in WTP positioning from DUB, GOT, OSL and LIN on the Sunday before the morning flight on the Monday from Heathrow direct to Seattle (BA53). £1075-1175 range.
Cheapest business fare to Seattle I can find is £2400+ ex-LUX. Save around £200 going to YVR, but you'll arrive in Canada in the evening (there's only one flight a day now on an A380 arriving at 6:45pm).
London business class is coming out in R class at £4k+ via DFW, or £2950 in WTP to Vancouver.
Good luck!