Ramirez, 26, posted a 4.91 ERA with eight strikeouts in six appearances this season after making the first Opening Day roster of his career. The side-winding righty had just two scoreless appearances.
Hembree, 27, has turned in four scoreless appearances for Pawtucket this season while striking out nine and walking zero in five innings. He appeared in 22 games for the Red Sox last season, posting a 1.50 ERA and .218 average against in his final 21 outings.
The Red Sox acquired Hembree along with lefty Edwin Escobar from the Giants for Jake Peavy on July 26, 2014.
• Lefty Eduardo Rodriguez will make another start at the club's Spring Training complex on Saturday rather than beginning his Minor League rehab assignment for an affiliate.
"That will be five innings up and down, 70 to 75 pitches," said Farrell. "And then at that point, we're hopeful that he would get out to an affiliate. But that will be based on how his work week goes this week, and it's not so much from an arm or a pitching standpoint. It's the agility, the PFP, getting off the mound and gaining confidence in that area."
Rodriguez suffered a patella subluxation in his right knee on Feb. 27.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, follow him on Twitter @IanMBrowne and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.