What you can do is,, slice the flush line inside the hull, put a flush adapter in-line and a shut off valve behind the flush adapter. Use the shut off valve when flushing and turn it back to the open position when not flushing as this line need to be OPEN under normal operation. You will need to CAP or PLUG the flush adapter as it would need to be closed during normal operation.
Or, buy extra blocks and make the outer edges longer on the floating dock. This would allow you a place to stand and yet make it no harder to launch and retrieve the ski.