Peters comment a few posts ago is very valid. If you are not going to use an ICE why not just use an IAP programmable chip such as the Philips P89C51Rx2 or the Atmel T89C51RD2. I'm sure other manufacturers have caught up as well. This will allow you to program at will through the serial port. At least for the Philips chip, you can forget all about pulling pins high and or low in order to be able to program, it can be done software only.

Erik