It really depends on the sample you want to track but here's what I would try in this case:
Use the BiDiFollower prototype after the Sample to track the amplitude envelope, the individual Attack and Release control will be handy. Then insert a Difference prototype, I think by default this will add a 1 samp delay and will subtract the delayed input from the input. The output of the Difference prototype is your velocity. Now you could use a threshold prototype to filter out only the attack of each hit. Depending on your sample this can be difficult, sometimes you will trigger twice or soft attacks will not get triggered. You have to see what fits. Use the output of the threshold and multiply it with the output of the Difference using a Product. This way only the velocity values which exceed the threshold will pass. Paste that into your desired velocity parameter field.
Not in front of Kyma now but I this should work or at least give you a starting point...
ps. You will get an overall 1 sample delay for your velocity values but I think that's ok :)