Wan 2.1 Flaccid Penis - Soft Cock, Dick, Lora, T2V, I2V

You can control the size pretty well by including "the penis is small, big, huge, etc". can add modifiers such as "very small", "extremely huge", "long," "thick", etc. Some examples of this are in the sample videos.

Seems to give good results with a strength of about 0.8 without degrading the overall quality of the video.