You could likely use RegEx in the tokens in place of the MID formula on the token calculator activity - but I think you'd still need to work the same way looping through the values.

I don't believe you can split a single value into multiple values using just RegEx in Workflow.

The SPLIT function can split a single value token into a multi-value token, but requires a delimiter character like a comma or pipe, it can't really do something like "split every nth character"

If you Google about splitting a string every nth character, there are a lot of coding examples - you could potentially find C# or VB.NET examples that could be implemented in Workflow.  That being said, the example I provided with loops took me 5 minutes to put together, and coding a solution would be longer.

Thanks for the help!  I haven't tested this out yet but I've got something in place using what you posted up there that should work once I iron out the kinks

Because I'm a big nerd and think this stuff is fun.  Here is a script to do it (using the "Script" activity).

This works exactly like my original comment does using Workflow activities - it just does it as a Script instead.  It loops through each value, grabbing the first 8 characters and leaving the remainder and looping back.

To test this, you just need the %(Test File) token, then the Script activity, and the Track Tracks activity.

Here's the Script: 

namespace WorkflowActivity.Scripting.Script
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Data.SqlClient;
    using System.Text;

    /// <summary>
    /// Provides one or more methods that can be run when the workflow scripting activity is performed.
    /// </summary>
    public class Script1 : ScriptClass90
    {
        /// <summary>
        /// This method is run when the activity is performed.
        /// </summary>
        protected override void Execute()
        {
            IEnumerable<object> array = (IEnumerable<object>)this.GetTokenValue("File List");
            List<string> newFileList = new List<string>();
            foreach(string value in array)
            {
                string newValue = value;
                if(newValue.Length > 8)
                {
                    do
                    {
                        string newValue2 = newValue.Substring(0, 8);
                        if(newValue.Length == 8)
                        {
                            newValue = "";
                        }
                        else
                        {
                            newValue = newValue.Substring(8, newValue.Length - 8);
                        }
                        newFileList.Add(newValue2);
                    } while (newValue.Length >= 8);
                }
                else
                {
                    newFileList.Add(newValue);
                }
            }
            SetMultiValueToken("New File List", newFileList, true);
        }
    }
}