An apparatus for guiding an elongated flexible instrument comprises a variable-length support assembly. The variable-length support assembly includes a first end, a second end, a plurality of support member pairs, and a plurality of eyelets configured to receive the elongated flexible instrument. Each support member pair comprises a first support member linked to a second support member, and each of the plurality of eyelets is movably coupled to at least one of the plurality of support member pairs along a longitudinal central axis between the first end and the second end. The variable-length support assembly is configured to selectively transition from a compressed configuration to an expanded configuration along the longitudinal central axis, and the plurality of eyelets are adapted to support the elongated flexible instrument as the elongated flexible instrument is advanced along the longitudinal central axis. Each of the plurality of eyelets includes a tapered alignment member configured to contact a tapered alignment member of an adjacent eyelet to move the plurality of eyelets into alignment along the longitudinal axis as the variable length assembly transitions from the expanded configuration to the compressed configuration.