I don't believe anyone else is involved but Heaney, the "consortium" angle was only made up to disguise himself because he got roundly panned when he was 'outed' before the bidding process. He had Abe but that was only as a lender not a joint enterprise, Abe was no more a partner than Nat West would be if they lent him the money (not that they would, he's a massive credit risk).
Even if he wasn't 'winging it' solo (and why would everything stall on a Heaney land sale if there were others involved) Stapleton doesn't have the £5m required. I think there was some role for him somewhere with Heaney but not as an investor, but then what does anyone know about the whole horrible murky set-up, all that we've found out has had to be dragged from their iron like grip.