Another obvious option: One of the hottest Mariners players, but he may be better suited in the outfield
As the team expects Locklear to fill in for France, there are still doubts given the lack of experience above the Double-A level. This is where they could turn to one of their hottest players, and someone that has also kickstarted this offense in recent weeks.
Luke Raley has been playing both corner outfield and first base this year. Though he has been relied upon more in the outfield as of late, especially with France's bat really coming alive, Raley could fill in at first base while giving some of their more experienced bats (Canzone and Haniger) an opportunity to get hot. The slugging lefty has cooled off a little in recent days, but in his last 30 games, he is still slashing .280/.343/.516 with six home runs and 13 RBI.
Raley is a sort of Swiss army knife that Servais loves. Raley can fill in at three different spots and could definitely be the answer if someone like Canzone or Haniger get hot and Locklear struggles to adjust to the Major League pitching. But with how comfortable Locklear looks and how bad Canzone and Haniger have been, he might be in the outfield quite a bit.