14.04 - No Audio over HDMI on nVidia Optimus

I have a Dell L502x laptop with Nvidia GT525M (Optimus) on Ubuntu 14.04. HDMI video works with nvidia 352 proprietary drivers, but the audio card is not detected. I don't see HDMI Audio listed in Sound playback settings, and lspci (and lspci -H1) show only the Intel Audio card.

Output of lspci -H1:

00:00.0 Host bridge: Intel Corporation 2nd Generation Core Processor Family DRAM Controller (rev 09)
00:01.0 PCI bridge: Intel Corporation Xeon E3-1200/2nd Generation Core Processor Family PCI Express Root Port (rev 09)
00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
00:16.0 Communication controller: Intel Corporation 6 Series/C200 Series Chipset Family MEI Controller #1 (rev 04)
00:1a.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #2 (rev 05)
00:1b.0 Audio device: Intel Corporation 6 Series/C200 Series Chipset Family High Definition Audio Controller (rev 05)
00:1c.0 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 1 (rev b5)
00:1c.1 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 2 (rev b5)
00:1c.3 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 4 (rev b5)
00:1c.4 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 5 (rev b5)
00:1c.5 PCI bridge: Intel Corporation 6 Series/C200 Series Chipset Family PCI Express Root Port 6 (rev b5)
00:1d.0 USB controller: Intel Corporation 6 Series/C200 Series Chipset Family USB Enhanced Host Controller #1 (rev 05)
00:1f.0 ISA bridge: Intel Corporation HM67 Express Chipset Family LPC Controller (rev 05)
00:1f.2 SATA controller: Intel Corporation 6 Series/C200 Series Chipset Family 6 port SATA AHCI Controller (rev 05)
00:1f.3 SMBus: Intel Corporation 6 Series/C200 Series Chipset Family SMBus Controller (rev 05)
01:00.0 VGA compatible controller: NVIDIA Corporation GF108M [GeForce GT 525M] (rev a1)
03:00.0 Network controller: Intel Corporation Centrino Advanced-N 6230 [Rainbow Peak] (rev 34)
04:00.0 USB controller: NEC Corporation uPD720200 USB 3.0 Host Controller (rev 04)
06:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 06)

Output of aplay -l:

card 0: PCH [HDA Intel PCH], device 0: ALC665 Analog [ALC665 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 1: ALC665 Digital [ALC665 Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

It seems to me that the device 3: HDMI 0 [HDMI 0] listed above corresponds to the audio device for the display port and not HDMI. In my laptop, the HDMI port is connected to the nVidia GPU, and the display port is connected to the Intel GPU.

With the open source driver, an nvidia audio card is listed by lspci -H1 but not in lspci.

01:00.1 Audio device: NVIDIA Corporation GF108 High Definition Audio Controller (rev a1)

However, HDMI video is corrupt with the nouveau driver, so I have to use the proprietary driver.

Is there anything I can do to get HDMI Audio working?

I should note that HDMI Audio works fine in Windows.

Edit

The workaround suggested in https://askubuntu.com/a/660910/489853 solves the issue temporarily; it needs to be applied after each reboot. Any suggestions on how to turn that into a script that can be run during startup?