VSCode Custom Variables in Launch Settings?

Is there a way to add custom variables that I can use in my launch.json settings for debugging in VSCode? Currently, the only way I have found is to add them to my workspace settings and refer to the from the ${config} predefined variable.

I'd like to define variables/properties in the launch.json and use them. Here's an example of what that might look like if I wanted to add myCustomVar to all my URLs:

{
    "version": "0.2.0",
    "myCustomVar": "my_value",
    "configurations": [
        {
            "name": "Page 1",
            "type": "chrome",
            "request": "launch",
            "url": "http://localhost/page1.html?customVar=${myCustomVar}",
            "sourceMaps": true,
            "webRoot": "${workspaceFolder}/dev"
        },
        {
            "name": "Page 2",
            "type": "chrome",
            "request": "launch",
            "url": "http://localhost/page2.html?customVar=${myCustomVar}",
            "sourceMaps": true,
            "webRoot": "${workspaceFolder}/dev"
        }
}