I haven't run a sponsored plant in years (mostly because they want a separate journal), but the one I did was a Brooklyn Sunrise auto back in 2018:
Hello again guys, it is that wonderful time again - The Comparative Grow And we have wonderful news this time – we have 2 Comparative Grows running side by side :) To be clear, if you enter both Comparatives, then you MUST post on both Comparative threads, and if you only join this Comparative...
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We all got to post in one thread so they didn't need us each to run one each. All that to say I don't think I've seen a sponsored group auto since, but no reason you can't suggest it! Especially since there are some amazing auto growers on the site (you included!).
@Carmen Ray (new MOTM!) will be running some sponsored autos, but it's not a group thing: