C# - String Replacements For Word Merge

using asp.net 4 we do a lot of Word merges at work. rather than using the complicated conditional statements of Word i want to embed my own syntax. something like:

Dear Mr. { select lastname from users where userid = 7 },
Your invoice for this quarter is: ${ select amount from invoices where userid = 7 }.......

ideally, i'd like this to get turned into: string.Format("Dear Mr. {0}, Your invoice for this quarter is: ${1}", sqlEval[0], sqlEval[1]);