No, when you buy on CS it goes into plan. When you transfer shares in from a brokerage it goes into book.

So say you have 100.5 shares in plan, and want to switch to book (which can only hold whole shares). CS will switch the 100 shares to book, and sell the .5 share. Unfortunately, CS has a fee for selling stock, which I believe is $25 per sale (set price, regardless of how small or large the sale is). Since selling .5 of a share is only about $11 at current price, that $11 would cover the sale fee, but you wouldn’t need to pay the difference, above $11. So essentially, you forfeit the fractional share.

Transferring shares from a brokerage to CS is a better way to go about it. Plus, with a brokerage you can time your buys when the price dips. Buying directly through CS only happens twice a week, so it could be a couple days between placing your buy order, and it being filled, and the price could change during that time, which is out of your control.