How to customize configurationSettings attribute

I'm sorry, I'm not going to watch your screencast; please ask your questions as text. To change that option programmatically, locate the configuration you need (for example, using RunManager.getConfigurations()), then cast it to RSpecRunConfiguration and call the setCustomSpecsRunnerPath() method on it. Note that you'll need to add the dependency on the Ruby plugin to your plugin.xml and to add its jar file to the classpath of your IntelliJ IDEA SDK.

How to "Note that you'll need to add the dependency on the Ruby plugin to your plugin.xml"?

Ok, I find following answer:

Plugin Dependencies

In your plugin, you may depend on classes from other plugins, either bundled, third-party or your own. In order to do so, you need to perform the following two steps:

• Add the jars of the plugin you're depending on to the classpath of your IntelliJ IDEA SDK. (NOTE: Don't add the plugin jars as a library: this will fail at runtime because IntelliJ IDEA will load two separate copies of the dependency plugin classes.)
• Add a <depends> tag to your plugin.xml, adding the ID of the plugin you're depending on as the contents of the tag. For example:

  <depends>org.jetbrains.idea.maven</depends>

To find out the ID of the plugin you're depending on, locate the META-INF/plugin.xml file inside its jar and check the contents of the <id> tag.