Workflow doesn't seem to have a Regex Escape function, but VB.NET does.

Add a script task ahead of the regex lookup. Import System.Text.RegularExpressions, then use Regex.Escape() to escape any Regex special characters from the token value and return the results as a new token to use as the pattern in the Pattern Matching activity.

In the Import section:

Imports System.Text.RegularExpressions

In the Execute sub:

Dim searchFor AS String, searchForRegex AS String
searchFor = GetTokenValue("searchForTokenName")
searchForRegex = Regex.Escape(searchFor)
SetTokenValue("searchForRegexTokenName",searchForRegex)

Then just update the Pattern in the Pattern Matching activity from %(searchForTokenName) to %(SearchForRegexTokenName).