The Pilgrims trailed to Lee Beeson's 35th minute header, but Miller nodded United level four minutes later and Sanders headed home Gary Mills' neat assist eight minutes after the break.
It was another useful workout for the Pilgrims, who fielded trialist winger Billy Bennett, against a side featuring ex-Boston players Beeson, Nathan Stainfield, Chris Hall, Dan Cotton, Danny Steadman, Gary King and Tony Battersby.
Boston (4-3-3): Sam Vince; Peter Bore (Conor Marshall 56), Scott Garner (Stefan Galinski 56), Carl Piergianni, Netan Sansara; Ian Ross, Gary Mills (James Reed 56), Ben Milnes; Spencer Weir-Daley (Ben Fairclough 56), Charley Sanders (Jordan Nuttell 56), Ricky Miller (Billy Bennett 56).
Referee: Josh Smith