Get SiteConfig variables inside _config.php - php

Question

In SilverStripe 3.4.1 I want to control _config.php file values through the Admin settings. I want to set some variables in Admin > Settings > MyTab and then access these variables in _config.php.
Is there a way to access SiteConfig variables in the _config.php file?
I tried to use several different ways to get the config data:
Config::inst()
print_r/var_dump gives all the values as an array
Config::inst()->get($this->class, 'PropertyName') or $this->config()-> get('PropertyName')
Returns empty
SiteConfig::current_site_config() or any other similar variations based on the previous two
Internal Server Error
The reason I want to do this is I have a plugin that replaces some SilverStripe default action but it requires some data to be inserted. If this data is not inserted it should stay as default.
Here are some resources I have read through to try to find a solution:
http://api.silverstripe.org/3.3/class-Config.html
https://docs.silverstripe.org/en/3.0/topics/configuration/
https://docs.silverstripe.org/en/3.4/developer_guides/configuration/configuration/
https://docs.silverstripe.org/en/3.4/developer_guides/configuration/siteconfig/

Answer 1

The issue is DB::connect is not called at that stage in _config.php. Therefore we cannot retrieve items from the database.
What we can do is call DB::connect in our _config.php before we retrieve our SiteConfig.
Assuming our database config settings are stored in $databaseConfig, here is the code to fetch our SiteConfig:
DB::connect($databaseConfig);
$siteConfig = SiteConfig::current_site_config();
Then we can retrieve SiteConfig variables like so:
$siteConfig->Title;