Soap Hole
Step 1: Drill a hole
Drill a hole through the center of a bar of soap about the size of your dick.
The larger the bar of soap, the better, and better to err on the side of a too-small hole rather than a too-large one.
Step 2: Fill the hole
Get the soap wet and pump away. The edges of the bar of soap feel like a woman's lips squeezing gently down on your cock.
When the hole gets a little to big to stimulate your cock, just use it to bathe.