How to transfer cash into an investment account without showing income

I need to add cash to an investment from an outside source that is NOT income. I do not want it to reflect in a category (i.e., income/expense) but just want it added to Net Worth (balance sheet). But the investment account has a linked checking account, so the investment account doesn't have the option of "Cash transferred into account" in the Enter Transactions screen. How can I reflect this incoming cash keeping it off the "income/expense" so it just directly increases Net Worth?