You can use CustomValidator and write your own verification code. Client code could hypothetically access each text field and check for regular expression ...
http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.customvalidator.aspx
A simpler solution, if you do not want to include the regular expression in 4 places, is to save the regular expression in the code and apply it to all validators during page loading? Not perfect soln, but will work. You can also apply the standard error message and other formatting options in the code.
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