1) Create an investment account especially for this activity. DO NOT
make it a "Single Mutual Fund" account.  DO NOT link it to a checking
account.  DO make it a "Tax Deferred or Tax-Exempt" account. DO make
transfers into the account non-taxable.

2) Create an INCOME category "Employer Defined Benefit Contrib"
(abbreviating as necessary. DO NOT associate this line with a Tax-Line.

3) Create a memorized transaction in an existing cash-type account.
The transaction will have a net zero amount.  The splits will consist
of  an line for the "Emp Def Contrib" (or whatever) category, with an
appropriate amount AND a 2nd line to to your Investment account (step
1) with a negative amount.  The net will be zero. Don't worry about the
negative sign, it'll work.

4) Schedule the transaction to occur each payday.

5) After running the transaction to deposit the employers money in your
investment account, go to the investment account and record the
appropriate investment purchases.

QED