Would it be difficult? If you market to consumers, you could give businesses a cost over the phone just like any other business, just on a per person level.
The next challenge is non-payment of premium. Lets assume Companies A, B, and C each respectively insure "Hank" respectively for 50%, 25%, 25%. They respectively pay $50, $25 and $25 per month in premiums to PoolingEntity. What happens when any of A/B/C fail to pay a premium? The insurance contract would eventually be terminated for non-payment (after a statutory notice period), and poor Hank would be back to being uninsured.
Technologically, I think it could be done. But the legal, regulatory, and administrative complexity would need to be addressed.
Separately, a great resource for reading up on where/how Americans get their healthcare coverage is the Kaufman Family Foundation. Many Americans have more than one source for their coverage. https://bit.ly/3KazKNN