I thought of that, but isn't $1,000 also embedded in a bar code at the bottom of the voucher?

Doesn't look like it on mine.  Just ssn, first 4 letters of last name and the year and some stray numbers that don't match anything.

You can pay directly here instead:

https://www.irs.gov/payments

Or print a blank voucher and write in the correct amount . you can obtain  blank IRS Form 1040-ES from the IRS. The form and instructions are at this link:  <a rel="nofollow" target="_blank" href="https://www.irs.gov/pub/irs-pdf/f1040es.pdf">https://www.irs.gov/pub/irs-pdf/f1040es.pdf</a>

Do not send in a voucher that does not match your actual  payment