A guiding accessory, for use in conjunction with a guidewire and a catheter of an implant system, facilitates passage of an elongate and flexible conductor of a relatively compact therapy delivery device to an implant site, for example, within the cardiac venous system, when a therapy generator of the device is held within a distal portion of the catheter, and the catheter, device and guiding accessory are advanced along the guidewire. The guiding accessory includes a helically extending wall that forms a lumen within which the device conductor and guidewire extend. After advancing the catheter, guiding accessory and device to the implant site, the helically extending wall is unwound from around the device conductor, for removal, preferably, by pulling proximally on a tension line, which is attached to a proximal end of the wall.