Based on prior knowledge and analysis of the relationship between BMI and the presence of diabetes, I can generate the following dictionary:

```json
{
    "yes": [25.0, 27.5, 32.0, 35.5, 38.7],
    "no": [20.2, 23.9, 27.1, 29.8, 31.2]
}
```

In this dictionary, the "yes" key represents the target class where the person has diabetes, and the "no" key represents the target class where the person does not have diabetes. The values for each key are lists of typical BMI values for each respective target class.