Is it possible to mount a volume to a custom drive prefix, e.g. "myDrive:\"?

Am I just a dreamer, or does something like this exist?

No, you cannot. It is called a drive letter for a reason.

The command myDrive: gives the error

'myDrive:' is not recognized as an internal or external command, operable program or batch file.

Note that is does not have to be a letter in the traditional sense. You can call your drive [:, for example.

DOS allowed you to use all ASCII characters between A and ` (both inclusive), giving you a total of 32 different drive letters. I am not sure how to access the last 6 on Windows though.

The closest you can get to your "dream" is mounting. For example, you can mount a drive (a partition, actually) in the folder C:\myDrive.

Another "solution" that will work for the Windows Explorer is adding an expandable string value to the registry key

HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\User Shell Folders.

This is where the actual locations of Desktop, My Music and such are stored.

You can create custom named "drives" using the PowerShell provider system. You would do something like

PS> New-PSDrive -name myDrive -PSProvider FileSystem -Root "F:"

You would then access the files/directories under that same drive like

PS> dir myDrive:\whatever\foo

It wasn't clear from your question if you were in a scripted/console environment or if you wanted to see this in Windows Explorer specifically. Also, I assume you were talking about a filesystem "volume". The PowerShell provider system also supports other kinds of providers.