All you can do is make your view size so huge that it won't fit on most people's screens - and that won't work when people have resolution of more than 1024x768.
Icons sizes are actually a client option, which means it's the player who gets to decide and not the designer. This might change in the future, but for now you're stuck.
Well, aside from all the negative responses, i can advise you that making each tile using tiny 2x2 pixel blocks would give the visual effect of 16x16 turfs, or you can design your 16x16 images, and then tile them into 32x32 turfs. sorta like this....
____
|12|
|34|
It is also possible to change the default movement to allow for smaller steps.
