The flow rate from the shell garage I go to is fine - some are way too fast but you can moderate it easily with your hand. Perhaps redesigning the handle as above would allow a more easily variable flow rate.
Shorter nozzle is a good idea.
Pay at pump essential if within your remit.
I want to kill the thing outside that's singing loudly and off key.
If necessary, the pump should be protected from diesel spillages from the tin can brigade and the route out of the station could have a isolated bike route or a surface which we can grip on regardless of diesel to allow us to not worry about skidding due to people overfilling.
The pump should also have a small area which is covered and only open towards the rider to allow us to put gloves in it without risk of them blowing away and being purposely stood on by an arrogant Audi driver (GRRRRR) and a filler cap with keys attached which isn't going to attract thieves as easily.
Supply of paper towel to immediately remove spillages is important.
A lot of the ideas presented are a solution to problems most riders work around to the point where we don't think about it. A short nozzle is a good idea but frankly it's not hard to just withdraw it slowly, just being able to modify the flow rate easier whilst sat on the bike would be useful in order to allow brimming of the tank. In order to make a station rider friendly, the ability to pay without having to remove hat and queue, sweating like Jacko in Mothercare is most important. A supply of tissues for small drips on the paint is useful, a gloves compartment built into the pump is very handy on windy days.
What's most important is that car drivers can not use the pump - some bollards would be useful although they may well exclude trikes.
Perhaps even a small shampoo dispenser and tap for those with teddies as pillions...
EDIT: If you make a shorter nozzle, you may have to remove some weight from the other end as it may well become more imbalanced than it already is.
EDIT EDIT: Don't rely on anything magnetic to make an idea work - many of us have plastic tanks. Also remember that some of us were daft enough to buy a BMW and fill from the side (would still benefit from the above though).