Envelopes With Vst Instrument

I work on a MAC and have the Bismark bs-1 VST loaded in instruments.
This works good and I can load soundfonts (SF2) and use them in my song.

The only thing I don’t get is: How can I create an envelope for a VST instrument???
Strings are endless repeating I want to make them shorter en make volume curves.

I saw Vsampler for Windows, it looks it had an option for creating envelopes.
Are there any other VST’s wich can do this? (For Apple Mac)

Thanx

Native Instruments Kontakt can.