From where Niel stands, head East as far as you can and then North as far as you can to get to the next battle.

Battle: Worker Tibor (1200 Poke)
Opponent: Sandile Lv 30, Drilbur Lv 30

Head South and then West all the way, then go North, West, and lastly South twice to reach battle 5.

Battle: Worker Pasqual (1200 Poke)
Opponent: Drilbur Lv 30, Baltoy Lv 30

From there, go North, and then all the way East for the next battle.

Battle: Worker Friedrich (1240 Poke)
Opponent: Sandile Lv 31

Next go West twice, South once, then West again and finally North to reach the seventh Gym Trainer battle.

Battle: Worker Maynard (1240 Poke)
Opponent: Drilbur Lv 31

Finally, go South once, East once, South once (pink escalator), East a second time, and then North once (pink escalator) to reach Clay at last.  Be forewarned, the man has a monstrously powerful team in no small part thanks to his Excadrill.  Don’t expect this to be any easier than dealing with Elesa- it’ll just be a more straightforwards hard battle than an annoyingly frustrating one.