When using Outsourced PO's Tami, the Purchase Account is the WIP account (in your case the Labour Variable Overhead account) and the Variance account is the Labour Variable Overhead Variance account. These should be defaulting in if they are set at the item level and all your other Outsourcing settings are set properly.
When you post a receiving transaction on an Outsourced PO, the WIP account is debited and Accrued Purchases is credited. The variance account would come in to play when you match an invoice to the receipt, if there's a difference between the receipt price and the invoice price.
So, if you are manually entering these accounts in the PO, then your Labour Variable Overhead account would be your Purchases account and the Labour Variable Overhead Variance account would be your variance account.
Make sense?