Docker for Windows - Install certificates using sn.exe / Strong Name utility - windows

Question

We have a Docker image that we use to build our Visual Studio solutions. This works great. Now we have some solutions that require a key. To install the key you use sn.exe, but Microsoft has gone through great lengths to make sure human input is needed, namely the password..
The image is based off FROM microsoft/dotnet-framework:3.5
I tried several tricks, especially from this Stack Overflow thread: Auto-entering Password In Sn.exe
The last answer is mine (Thomas Rijsewijk). At least I have a working way to install the key automatically, but somehow SendWait doesn't work in Docker, or Docker for Windows, or microsoft/dotnet-framework:3.5 docker image.
# ---------
# Import all certificates in C:\keys
# ---------
[void][System.Reflection.Assembly]::LoadWithPartialName("'System.Windows.Forms")
[System.Windows.Forms.SendKeys]::SendWait("hello")
When I run this I get "Access Denied":
Exception calling "SendWait" with "1" argument(s): "Access is denied"
At K:\install-certificates.ps1:51 char:1
+ [System.Windows.Forms.SendKeys]::SendWait("hello")
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : Win32Exception
As an alternative I tried SendKeys() from WScript.Shell:
$wshell = New-Object -com wscript.shell;
Sleep 5;
$wshell.sendkeys("test");
Again, this works perfectly on my machine (Windows 10 up to date) and an up to date Windows 2016 server. But NOT inside the docker image: nothing happens, no error but it's not entering "test" either.
Lot of talks about automating powershell, but basically I don't really care HOW I install the certificate when building my docker image, I just want it installed. I install the certificate locally using
Start-Process "C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin\sn.exe" -ArgumentList "-i `"D:\key.pfx`" VS_KEY_XXXXXXXX" -NoNewWindow;
At this point, it asks for a password which makes it impossible to use with docker build.
I did a whole lot of searching on Google and SO, I'm surprised to see that nobody else tried to install a key using sn.exe.
PS: Yes, I know VS_KEY_XXXXXXXX is not a valid VS_KEY. I already have a working mechanism for extracting the right VS_KEY, but that's out of scope of this question.
PPS: Yes, I know I could manually running the docker, install the certificate and manually commit and push the changes. But naturally, I want it to originate from my Dockerfile