Hillson, a former Lothians champion, closed with a two-over 74 for a nine-over 297 and was joined on that mark by the 2008 Scottish Boys' champion Stewart, who sagged to a 78.
The Scottish duo finished 12 shots behind Hampshire's Darren Wright, who eased to a four-stroke victory with a 72 for 285.
Colville Park's Ross Kellett, winner of the Tennant Cup last weekend, signed off with a 77 for 301 and shared 25th spot.
The win was the biggest victory of 21-year-old Wright's career and he said: "I came here to prove I can compete with the best and this means everything to me."
Meanwhile, Raymond Russell had to settle for a share of fourth in the Alps Tour's Mirabelle International Open in France yesterday.
The former European Tour champion, who was sitting just a stroke off the pace with a round to play, closed with a level-par 72 for a 16-under 272.
Prestonpans pro Russell, who was a winner on the Alps circuit back in April, finished five shots behind Spain's Juan Antonio Bragulat, who eased to victory with a 68 for 267.
Perth's Gavin Dear hit a 69 and shared 11th spot on a 275.
Back on home soil, Steven Taylor notched his first Tartan Tour win of the season in the Heil Bathgate Pro-Am.
The Bothwell Castle pro, with six previous top-tens on the domestic circuit this year, made the breakthrough with a sparkling eight-under 63 to bank the 1154 top prize.
Taylor won by three shots from former Scottish PGA Matchplay champion Mark King. In the team event, runner-up King led the Eco Building Solutions amateurs to victory on a card countback after a 54.