There's a variable in the config.ini (on the Portal) that will accomplish this.
On the system where the Portal is installed:
1) Navigate to ~Foundstone\Portal\Include
2) Open config.ini for editing
3) Locate and un-comment (remove the semi-colon) the following line:
; disable_quickscan = 1
4) Save config.ini
5) Logout and back into the Portal
Uh oh! What version do you have? I just tested it out on 6.8.8 (works) and on 7.0.4 (doesn't work). I will get a bug opened to fix it, but we've missed the 7.0.5 patch, so it will not be until March 2012 until you would see any fix for it. If this is urgent for you, then open a Service Request, and PM me the SR #. I will pursue a hotfix for you.
Aha! I thought I had seen it before!!! apologies, I usually add version details when required - I am indeed running 7.0.4 :-) Its not critical - just one of those little things I want to get tidied up!
Good News! I don't know what I did, but I must not have saved the config.ini when I did my test. I just tried it again in 7.0.4 and it's working w/ the above steps to disable it from the top of the GUI - there is a problem in Manage Assets however... looks like you can right-click the asset and quick-scan it. That will be fixed in 7.5.
Sorry for confusion.
It looks like I was being blind... I had searched for quickscan aswell! Definitely there, so basically the gist of this post:
Q: I cant find quickscan option in config.ini
A: Look again. tada!