I believe you would need to transfer the HSA (or whatever funds from it you want to use for this) into a self directed IRA, and then make purchases from there. After that you could decide to try and go the self directed LLC route to DRS, or find another custodian (risky after Ally and Mainstar). Disbursing funds to purchase shares with Cash is also an option although rarely appealing.

Maybe if you have a fever, and the only prescription is more DRS

(sorry, couldn't resist)

When I have spoken to apes with HSAs before I remember the solution being a rollover into a SDIRA to then move into DRS.

The other option would be to take the tax hit. You can either take an early distribution (sell) or an in kind transfer (move the stocks to a cash account). Not sure if HSAs can do an in kind distribution, it may be you have to move them to an IRA first.