Reverse Ground Clamp for Ladder Tray

We have the clamps that mount on the outside of the ladder tray, but there is over 800ft in a round building around magnets, so not advisable at this stage of the game.

This is not clear, at all. Not sure how you can solve fill calculations unless the conductor is outside of the tray? How that fits in with your installation in a round building with magnets, copper wire, aluminum tray...?

Perhaps you are taking the fill calculation to impractical detail, the wire fits or it doesn’t, if you have maintained spacing, the ground wire could block some air flow.

Is there a problem with lugging off the earth and using a Stainless steel bolt, nut and spring washer to attach it to the tray, a high grade stainless is non magnetic so no problems from magnets and it is a good firm connection when tensioned up correctly.

KISS do it once and forget it once installed. Or you could spot weld the bolt to the cable tray.

You could try stainless steel carriage bolts,nuts,and washers if the local AHJ approves,even though it is not a listed method.

The button head would be placed inside,and the rest outside.The head would not interfere with the calculation.

Does the ladder tray have a solid bottom or a rod bottom?Only the discontinuous sections need to be bonded to each other.

An image or sketch of the tray would help to determine your needs.

You could place the bolt head of the clamp below the rungs of the tray.

Here is a link:

https://help.elecdes.com/paneldes/how-to/wire-and-cable-routing/use-the-nec-code-to-calculate-raceway-filling

and another one:

https://electrical-engineering-portal.com/practices-for-grounding-and-bonding-of-cable-trays