The only option is to make his life difficult. I would advise rushing, but dwarves aren't built for that. Maybe it's better to try another race?
If you still want to play as dwarves, then defense is key – fight to the last, use the resurrection rune, and rely on luck (maybe the harpooners will get lucky and deal significant damage to the horses without a luck penalty, and if you also have Carli). Use light magic and leadership – runic harmony.
Try to develop as quickly as possible (this is helped by the starting hero Carli with soldier's luck, archers, crippling strike, and a purchased cart). And use the speed rune. Fight somewhere around week 7.
In general, fighting to the last + the resurrection rune can really save you.