I modified your sample for this.
Steps to see what I am talking about (assuming office 2010):
1. run program
2. click Generate Data Fake
3. modify as desired, save and close
4. click View Template
5. Open Mailings ribbon
6. click Start Mail Merge > Step by Step Mail Merge Wizard
7. choose Letters
8. click Next: Starting document
9. choose Use the current document
10. click Next: Select recipients
11. choose Use an existing list
12. click Browse...
13. choose Sample\Data\MergeTemplateFakeData.xlsx
14. choose Sheet1
15. ensure First row of data contains column headers checkbox is checked
16. click OK
17. click OK again
18. in ribbon open Insert Merge Field dropdown
notice that the colons are removed from the merge field choices
19. after finishing click save (don't finish the mail merge in word)
20. click Generate and view the result
Sample_be9d2427.zip