Note that I don't see all of these players being part of the Pirates' bench going into the post-all-star break. However, a few of them will be part of the Pirates' bench and make occasional starts.
Tucupita Marcano, like many Pirate players, has fallen into a slump recently. After a strong start, he's now batting just .235/.285/.386 with an 80 wRC+. But he's displayed much more raw power than last season, and his .312 xwOBA (compared to his .291 wOBA) suggests a rebound for the utility man. He's been phenomenal at second base this year, though his shortstop defense is lacking. Though he hasn't played any outfield this year, he could be an option on occasion there as well.
Josh Palacios has been an outstanding minor league Rule 5 find. Palacios' overall numbers are not good, but like many players, he's been stretched thin because of the team's current lack of depth. Palacios could be an outstanding part-timer/pinch-hitter. He has five hits and a walk when he pinch hits and six hits and two walks in late and close situations. It also helps that he's made some highlight-reel plays and is generally well-received by defensive metrics.
Ji Hwan Bae
I think that Ji-Hwan Bae's recent struggles are partly because of him being asked to take on a greater role than he was originally expected to. At one point, Bae was providing the Pirates with a solid bat, hitting .275/.332/.369 with a 91 wRC+ prior to his massive slump. His speed is game-changing, so even while he wasn't providing much power, he made that .332 OBP a deadly weapon. Bae also looked like he was getting more familiar with the outfield. I think that if Bae is only asked to take on a part-time role, he'll figure things out once again.
Rodolfo Castro is still highly effective against LHP, with a .263 batting average and .909 OPS when he faces a southpaw. His defense at second base also hasn't been terrible. He's been about average with +2 defensive runs saved and zero outs above average. However, he has very clear weaknesses, like his sub-85 wRC+ against right-handed pitching and his -5 DRS/-6 OAA at shortstop. If a left-hander is starting pitcher or a Southpaw coming out of the bullpen, this is a guy you want to put in the game.
Look, I know people are tired of seeing Austin Hedges hit, I am too. He's on pace for one of if not the worst hitting season of all time. I'd be lying if I said Hedges and his sub-30 wRC+ weren't infuriating. But in his defense, his glove behind the plate has been the best in the league. Despite basically sharing the position with Jason Delay (who I see getting optioned once Endy is up), Hedges has +7 DRS, second to Giant standout rookie Patrick Bailey. However, his +10.4 framing runs lead the league by a wide margin. Hedges is having a poor season, even for his lowly standard with the bat, but his defense has been valuable to this pitching staff.
Connor Joe is very similar to Castro, except in the form of an OF/1B. Against right-handed pitching, he's hit a paltry .211/.296/.352 slasher with a 78 wRC+. However, when he faces a left-hander, we're talking about a guy who is hitting .276/.382/.517 with a 145 wRC+. That's the difference between one of the top 15 batters this year (comparable to Corbin Carroll or Matt Olson) and one of the bottom ten hitters ( comparable to Jace Peterson or D.J. LeMahieu). He's also been about an average defensive corner outfielder/first baseman.