I agree that this would be nice.

In the interim period of waiting for hopeful updates, it's not very difficult to add this yourself.  Your custom added controls will not show up on the ARIA Control Panel, but you could still add the opcodes and control them with your DAW and MIDI Controllers using an assigned controller to the sfz file.  One can find more information on working with sfz opcodes at the following links (and more if you do a web search).

http://drealm.info/sfz/plj-sfz.xhtml#what

http://www.plogue.com/phpBB3/viewforum.php?f=14

It's typically done with ampeg_ codecs..

Example:

<Controls>

//Amp EG
set_cc73=00
set_cc75=33
set_cc70=127
set_cc72=22

<global>

//Envelope Controls
ampeg_attack_oncc73=2.5
ampeg_decay_oncc75=2.5
ampeg_sustain_oncc70=100
ampeg_release_oncc72=1.5

 <master>

etc...

When choosing CC controllers double check that they're not already being used by the instrument that you're tweaking, or you could end up with unwanted conflicting effects'.

Experiment, but do remember to backup your original sfz files.

I must say, I fully agree. Had great expectations for Garritan, but the apparently built-in attack delays with various of the strings made it impossible to use the program if I was using other sound libraries on other tracks and channels without the attack delays. I use a midi guitar input, so do not have the sophisticated midi controls on the hardware. Would seem to me that Garritan should be able to enable controls so that Garritan can play nicely with other sounds. Sigh. Garritan is simply going to put aside the interim. Would it be appropriate to notify potential users of the problem so they can delay purchase pending a fix? Two years is a long time to wait for a fix, and I must say I am disappointed that I cannot use the product in the interim.