JoPo, here's some other ways to get something similar:
1.) Use a multi-segment envelope to simulate what you want:
the FreeEnv from here:
http://cwmodular.org/html/multiseg.html
or these:
http://cwmodular.org/html/other.html
(the second module, bottom left corner shows an attack similar to what you are looking for, I think the same can be done for each stage)
2.) Add a delay to the gate signal before the envelope. This delays the start of the envelope, and you can then approximate the attack with a linear response.
(so: delay time + linear slope(with high slope) = estimate of the attack you are looking for).
I know these aren't ideal, and don't have "1 knob to adjust" the setting you are after, but they might get the job done for now, and you can hear roughly what the results would be.