Workaround for no checkbook control on Solo 401k ROTH sub-account

I have a Solo 401K with checkbook control for the master account. But my custodian does not allow checkbook control on designated ROTH sub-accounts. I’d like to convert funds from the master 401K account to the ROTH sub-account (pay the necessary taxes, of course) and then buy real estate with those ROTH funds. But without checkbook control, I can’t see how I can do that. Are there any workarounds?

I've seen examples with SDIRAs where the IRA owns an LLC which has a checking account; money is transferred to that checking account and purchases are made from there.

Is this a valid option for me? Or are there better solutions?

Thanks for any and all help with this question!