Chris1 I know that you can cum by using a classic vibrator vor ladies on the cage / belt ... it works if you have been locked for a very long time. Personally I would only do it with a waitst string so that your balls don't get set under so much pressure.
You can also use a relatively thin vibrator with a condom over it (hotta say that I never tried it) or a vibrating stick to massage your prostate and cum without having an orgasm. That is said to be very healthy.
Well, there are two different understandings of chastity ... the old one where chastity is also when you are not locked butlife a life without sex and masturbation ... like a monk ... and the new one is when you are locked but able to please your gf and so on ... or have an orgasm in chastity ... it's depending on what sort of understanding of chastity you have.