Black Jack "buy bets"

I work in a casino that offers a California version of BJ. The rules are: Dealer hits soft 17, BJ pays 6:5, double after split (except aces), split 3 times for total of 4 hands (except aces), double any 2 cards, late surrender.
There is a relatively new bet offered called the "buy bet". In California we have a 3rd party banker because the house is not allowed to bank the game. A rep from the corporation is always seated at the table. For a 5% fee, $1 per $20 wagered, they will play the hand (always according to basic strategy, factoring in their 5% payment, but they can only split once and can not double after a split) and the player assumes the dealers hand. Using the K-O count system, or the HiLo count system, what negative count is needed to overcome the 5% fee?

I forgot to mention it's mostly a 6 deck shoe and 2 decks are sometimes offered.

When you assume the dealer's hand, does dealer BJ pay 6:5? Can you split or double? If the answer is no to some of these, you probably can't overcome the commission.

I'm not sure I understand your question. When the players opts for a buy bet then they are hoping the dealers hand beats the buy bet. If the buy bet gets a BJ then the player owes the corperation 6:5. If the corp doubles or splits then the player wins or loses accordingly. The player has no control over the hand once the buy bet is placed.

Oh. Then I guess the count needs to be around -7 or -8 to overcome the commission. That's an estimate.