Has anyone found a good investment solution for a 401(k) plan with 2 - 5 participants? We would prefer not to have to set up separate brokerage accounts for each person because of what's involved in the deposit of contributions from weekly payroll. These plans are too small for most of the daily platforms we use for other plans.

How about one brokerage account? You would need to do quarterly vals though if you want individual direction.

I have a client that has no participant direction (which I think is a luxury for most people), and the val is done just once a year. This is often a good solution specifically for the reason you've identified.