You are free to use any ribbon riser that is ~50 mm long and has straight connection/is not angled. The case is made in a way it holds the riser by the PCI-E slot body and unless there's some weird stuff added to it, it should work okay. If you pick a riser that is fairly standard with the slot being in line with PCB and ribbon, the worst you may have to do is to detach the latch if it's too big, although there should be space for most of the latch types.
You should however look for reviews of specific riser to see if it is actually recommended or whether it's some off-brand no-name company that noone tried to use. We'll be revisiting this topic once we are ready to move forward with 3.0.
Thanks for the info.
As for the riser, atm I'm looking at the Linkup Ultra PCIe 4.0 Extreme - Straight Socket 50mm length. That is, provided I will be able to get an AMD RX 6000 card on thursday drops or an EVGA 3000 XC3 card someday.
In previous posts it's been hinted that this Linkup riser could need some mods to fit into the Sentry though. I was wondering if, in preparation for rev. 3.0, you were investigating the market and have found something PCIe 4.0 compliant&tested and totally compatible with the Sentry out of the box, no mods required.
Wishful thinking, I know.