XSI 5 - Character animation: add new bones to envelope.

OK, so I have rigged and skinned my character. Already adjusted all the envelope weights and such. Spent 2 days only to understand that I need one more bone to drive the envelope.
So how can I add a new bone to the envelope in XSI? In 3ds Max it is very easy to do, there is a button add bones . I couldn't find it in Xsi though.
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Fiery

Just do the Set envelopes again with you mesh selected and then pick all the bones you wish to add.

Ok I did all this and nothing happens.
My mesh is deforming as if I did nothing.
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Fiery

Nothing happens because the bones were added but no weight was applied to them.
You have to pick them and paint the weights on the envelope as needed.