Right now you have a % fee off delegators rewards its called commission fee and can be set from 0 to max_commission. Beside that fee there can be a second - flat fee that validator receives for his operations which is not % but simply a constant he defines in range from X to max_flat_commission. Before your delegators receive rewards this flat fee would be filled first every week and ensure you can sustain service and only then delegators would begin to receive their rewards. On top of that you would have this % fee you can define as 0 and threat as bonus.
Second option you can propose to have it on protocol level that all validators 1-100 receive some flat fee of the network for every week of operations without a downtime.
This fee would be small (not to cause sybil attacks), lets say 100 or 200$ a month, so its literary 0 vs what entire network earns and ensure regardless if you are big or small you can sustain operations and are not in a loss at least on the hardware.
TBH I am fan of a second option more because its incredibly easy to implement and solves the issue you presented at least to some degree then on top of that implement this proposal to have complete solution. (Just make sure in the proposal that it can be changed by governance automatically, so we do not have to make new proposals for flat fee adjustments)
You can call it Asmodat Fee 
in the final proposal I’d be honored