Hi nbongo, yep you have left it a bit late.. then again, there is no time like the present.
The itinerary calendar indicates where people are flying to, class of travel and those with an [L] next to their name have a lounge invite going spare. Site etiquette is that you drop them a message and ask
very nicely to be their guest.
As tonty says though the AU s and UC pax out there can only invite one guest in, so you will need to likely ask two people - I see only one with an [L] flying today

Pay access to the LHR CH is a possibility, it is always worth asking at the podium although it is very dependant on what mood the front desk staff are in and if there is going to be space... as you can imagine it does get busy in there at times.
£60 is not a bad price to pay for the amount of food and drink that could be consumed ): Failing that the no.1 lounge gets good reviews although it is no clubhouse

Hope you manage to get in somehow and enjoy your flight 8D