Double "T" nut

[Toolmaker51]

Yep, these extensions work. I do this on rotary tables, tilt tables and so on.
A good way to add stops outside the normal surface envelope too. Use caution though people, you'll generate a lot of leverage outside the t-slot; they can break. If you make these, fit them closely, so when under tension they contact a decent amount of the underside of t-slot to counteract tendency to tilt. A set screw in the inboard tapped hole helps too.
Spherical washers equalize contact between step block and part, at the nut. Nut needs to be paralell to upper surface of clamp, otherwise stud/ bolt are bending. https://www.carrlane.com/catalog/index.cfm/27025071F0B221118070C1C512D020609090C0015482013180B041D1E173C3B2853524A5D Maintain a minimum 2 or 3:1 clamp ratio.
I'd also recommend "rotary" t-nuts when you need additional clamping part way through a set up. https://www.carrlane.com/catalog/index.cfm/27225071F0B221118070C1C512D020609090C0015482013180B041D1E173C3B2853524A5C56
They drop in the t-slot instead of needing access from the open end of table.

Website supplied is not a recommendation of brand, just a very complete online catalog.
I am 100% cautious of where my tools are made though, the giant distributors don't always declare where items are sourced. Cheap clamp hardware is exasperating.
PM me and I'll provide reliable contacts that make and carry good quality components.
And to Jon, maybe contacting those to offer ad space would be worthwhile...$$.

I have no financial arrangements with any, probably why I have favorites.