The only way that I can see to make it a little more provably fair to investors is making a system of distributed server seeds, and giving access to each new server seed to a different big investor. That way you can even distribute the risk of holding everything on a single hosting service. So on each roll the central server asks to each seed server what's the hash for that roll of that user, and the seed servers answer with a corresponding hash which is then used to roll the final number.
Main drawbacks would be a lot of added complexity, maybe increased unreliability if you need all the servers up all the time, probably a cost/benefit ratio too high...
You can't rely on a single source for generation of the roll outcome.
A better mechanism would be to have 2 servers controlled by different people with each its own seed (this concept can be expanded beyond 2, but my example uses 2 for simplicity).
For any user, both servers have their own server seed and publish its hash as usual. The player can provide his client seed and the nonce is generated as usual too. When a player makes a roll, server 1 computes hash(seed1, clientseed+nonce) and broadcasts the hash to server 2. Server 2 then computes hash(seed2, received_hash_from_1) and returns to server 1.
Server 1 is the regular JD server operated and controlled by dooglus. Server 2 in this example is a server controlled by a third party, be it some form of trusted escrow or a large investor.
The last server to compute a hash, knows whether a bet will win or lose and can in principle feign a network interruption to not transmit bets that have an undesirable outcome. To combat this, other server(s) keep a log of all bets for which the hash was transmitted, but no reply was received. Servers will retry to transmit their hash to the next server in case of a timeout and prevent users from placing new bets until the previous one has resolved.
In this setup, there is no single party that has sufficient information to predict bet outcomes. With servers keeping logs of bets they receive and transmit, the system can be audited to ensure that no single party is witholding bets with undesirable outcome. Obviously, this is a relatively complex system and it introduces additional latency and potential failure if a secondary server is disconnected. But this is just a rough sketch, one could extend the system with numerous servers and some form of redundancy.
This setup would make JD (or any similar game) provably fair for its investors under the assumption that the operators of the servers are all independent and not conspiring together.