There is no point in me making suggestions as the free market will make the decisions, not you and not me.
If enough people like you are indeed requiring same day returns and if (a very big "if" here...) they are willing to pay some serious money for those tickets that makes the operation viable, there will be airlines willing to offer services. History, however, suggest that the limited demand requires fares that not enough punters are willing to pay.
But as you seem to be convinced that there is literally big money lying on the runway at IOM that airlines are simply too stupid to pick up, you could, for example, give Sun Air of Denmark of MHS Aviation of Germany a call. They operate 30 seaters in niche markets where serious money is paid for tickets (expect fares north of 200 GBP one-way).
PS: What you describe as a "sensible compromise" pretty much sounds like an unlawful collusion in violation of antitrust law as you apparently want two competitors to agree to not effectively compete.