I just did that half a year ago on a simple (stupid looking) mod on an old cabinet.
So what I did, having 3 fans of same brand/type running from one motherboard connector:
- Fan1 connected to molex plug, all wires.
- Fan2 connected in parallell, but feedback not connected.
- Fan3 same as for fan 2.
So - when the intention is that all fans should run at near full speed this is good.
If you intent the fans being run low speed, this is bad because there is a risk of stalling since the fan controller only get feedback from one fan.
Also - since this are somewhat risky, My setup was tested with a rude (very cheap) 12V supply just in case there is a short circuit. You probably do not want to risk your motherboard.