So, after looking at the picture a bit, it seems a very similar jump to the junker's gun jump can be made from the outer top guns to the lower guns.
Given that the current meta is that you shoot the gat first, and then you shoot the flak. This would allow 2 gunners to get 4 guns on the target. Strip the hull first with 2 gats, and then jump down to finish them with 2 flaks.
This may not work against squids or goldfish, due to their quick rebuild time. The delay between dismounting the gun, making the jump, remounting a different gun, and aiming on target would definitely be noticeable. The time taken to climb back up to the gats even more so. For this, the normal 1 gat, 1 flak would work, with the option of the pass being made on the left or the right. Against all the other ships though, it would be tough to get the hull up in time, and 8 flak shots would kill any ship, even the galleon.
Of course, provided the main engi isn't repairing anything at the time, the center gun would be great for a field gun, artemis, or banshee. Which would be used to provide some extra range/disable.
So even though five guns on a four man ship doesn't make much sense, if you stagger the fire times (like you do), it could be very possible to make use of all of them without ever having the pilot leave the helm.
Note: I'm talking about using exclusively flak instead of flak or mortar for 2 reasons:
The first being heavy ammo is common for both gat and flak, but not for mortar. Allowing the guns to be manned by engineers, rather than gunners. Which means in addition to having more repair and fire removal on-board, those 4 guns can now be buffed as well.
The second reason is that the mortar takes a few shots to sight in during most situations, which would add a considerable amount of time to required to switch from the piercing weapons to the explosive weapons.
