This accessory comprises a remotely steerable catheter (40) extended by a tip (50) comprising a base (52) to which the catheter (40) connects to and a cylindrical portion (54) defining a volume (56) suitable for housing the capsule (10). A sub-catheter (30) and the capsule are telescopically extendable with respect to the catheter between i) a retracted position and a deployed position wherein the capsule is removed from the connector and is carried by the distal end of the sub-catheter, and the distal end of sub-catheter and the proximal region (18) of the capsule being provided with disconnectable means of attachment (20, 36). The tip presents, between its base (52) and its cylindrical portion (54), a flexible portion (58) providing, between the base and the cylindrical portion, an elastic deformability in bending and compression.