Is there a way to create a string that matches a given C# regex?

My application has a feature that parses text using a regular expression to extract special values. I find myself also needing to create strings that follow the same format. Is there a way to use the already defined regular expression to create those strings?

For example, assume my regex looks something like this:

public static Regex MyRegex = new Regex( @"sometext_(?<group1>\d*)" );

I'd like to be able to use MyRegex to create a new string, something like:

var created = MyRegex.ToString( new Dictionary<string, string>() {{ "group1", "data1" }};

Such that created would then have the value "sometextdata1".

Update: Judging from some of the answers below, I didn't make myself clear enough. I don't want to generate random strings matching the criteria, I want to be able to create specific strings matching the criteria. In the example above, I provided "data1" to fill "group1". Basically, I have a regex that I want to use in a manner similar to format strings instead of also defining a separate format string.