Miller struck in the 35th minute as the Pilgrims sealed a narrow win over the United Counties League side.
A host of trialists and fringe players were on show for United at Chestnut Avenue, with Stefan Galinski making a welcome return from injury.
Boston (4-4-2): Sam Vince; Peter Bore, Conor Marshall (Stefan Galinski 46), Elliott Green (Netan Sansara 60), Nathan Fox; Ben Fairclough, James Reed (Ben Milnes 60), Alex Meaney, Billy Bennett; Charley Sanders, Ricky Miller (Spencer Weir-Daley 60). Subs (not used): Carl Piergianni, Ashley Timms (gk).
Referee: Damon Pywell