The function to turn power off a port can be accomplished, but only on a certain kind of hubs.
CASE_1: You have a hub that is an officially-certified bus-powered hub. According to USB specification v.2.0 for bus-powered hubs,
"Power to external downstream facing ports of a bus-powered hub must
see, section 184.108.40.206. This means that the hub must have "high-side" power switches, and hub controller IC must have means to turn these switches on/off. If a USB host sends USB command to reset its port with hub attached, the hub must turn VBUS power OFF on all downstream ports. Unfortunately, vast majority of "el-cheapo" hub manufacturers ignore this mandatory requirement, and have VBUS power derived directly from host power, from the cable. It is very unlikely that you can find the "correct hub" on store shelves. I would say "never". This leads us to Case_2.
CASE_2: You have a junk bus-powered hub with "captive cable", and it has an illegal ganged non-controllable power to its downstream ports. In this case you must have a computer that does have the power switching capability on its ports. This might be on many laptops, and maybe on few high-end industrial-grade desktop PC. Then, if you manage to perform internal port disable function on host controller, VBUS will be disabled, and hub power will be gone. Unfortunately this is very unlikely, since all ports are controlled by USB driver, which won't stop and will proceed with port enable, USB detection and enumeration, so VBUS will be enabled. So this is mostly a theoretical option.
CASE_3: Yet another way to disable VBUS on downstream ports of a hub is to have a version of self-powered hub (with power coming from AC-DC adapter) that has built-in downstream power switches, usually with current-limiting function. See Section 220.127.116.11 and Figure 7-43 of USB 2.0 Specifications, and also Section 11.11. Again, a self-powered hub is allowed not to have these expensive switch ICs, so vast majority of hub manufacturers skip this option, and put no control over downstream VBUS. Funny, the USB speculations still have a clause saying,
"Although a self-powered hub is not required to implement power
switching, the hub must support the Powered-off state for all ports."
see Section 11.11, third paragraph. I have never seen this kind of hubs. No wonder that you can seldom find ANY hub at local electronics store that carries USB-IF certification logo.
The only hubs that comply with Hub Port Power Control requirements are the hubs that are used in official USB-IF certification process, so-called "Gold Tree" devices. One of the "good hubs" was made by D-Link, however there is no guarantee that the off-the-shelf mass-produced variant has all power-switch ICs populated and not bypassed by either poly-fuses or just shorts.
So you are likely out of luck even in this case.
The last resort would be to cut the red wire in USB cable and put there a electro-mechanical switch, a relay, or a high-side switch, as suggested by Antonin. Then you need to find out some means to turn it off when PC goes to deep sleep, feed it from internal 5V rail, or something.