So, there’s a cheap way to do this, and an expensive but cool way to do this considering your setup.. love the 3090 miniATX by the way, it’s just so min/max.

Cheap and kinda janky- something like this: VIVOSUN 4 Inch 195 CFM Inline Duct Ventilation Fan Vent Blower for Grow Tent https://www.amazon.com/dp/B01M7S46YZ/ref=cm_sw_r_cp_api_glt_fabc_XXHXGVK1JX9S94VHC4HF

It’s janky because you need to run it off a 120v supply - but, it will get air where you need it, and it’s quiet. 200cfm is more than enough.

Cooler, and more expensive (if you go all copper - which you should...) but looks like a lot of fun is something like this build LTT did (2:30ish) https://youtu.be/qflqUpxTZP4

Copper rods aren’t too expensive, something like this might do the trick: (10pcs 1.2X3.2X500mm Flat Silver Electrode Low Temperature Phosphor Copper Welding Rods HL201 Self-fluxing Alloy Soldering Brazing By Keaiduoa https://www.amazon.com/dp/B07TH8STP4/ref=cm_sw_r_cp_api_glt_fabc_V4XNGNDK7HHXH7DKWMQD) But I could see this getting futsy really quick if you’re not aligned really well. So you may want to go with a much larger single heat sink to cover the vram and go with bigger flatter copper rods - all about the surface area. Anyway, the copper should xfer heat well down the rods to ostensibly another heat sink where you can put a fan.

Man, that looks like a lot of fun actually.

Or you could bite the bullet and spend the 1kish to water cool the thing like I ended up doing.

Good luck - let me know what you end up doing!