A single strand of speaker wire or lamp cord would be great.
I can vouch for that. I live some 35 miles from Cleveland and get excellent FM reception from every major station in town, and a few smaller ones as well (even on my 1965 Zenith MJ1035, which doesn't have the best FM front end or MPX decoder on earth) using only one conductor of a length of zip cord.
These days, one can usually get good FM reception in most metropolitan areas with simple antennas. This is in sharp contrast to FM's early years, when many smaller cities did not have local FM stations; the stations that were available, mostly in large cities, ran much lower power and were more difficult to receive. (There were exceptions, such as a 140-kW ERP [effective radiated power] blockbuster near Cleveland in the late 1960s, which had fantastic coverage of all northeast Ohio and probably 100 miles beyond in all directions; however, the station was ordered by the FCC some time in the 1980s, IIRC, to lower its ERP to 16kW vertical and horizontal [32kW total] to prevent interference to new stations on the same frequency [107.9 MHz] in cities such as Buffalo, Toronto, et al; this was an exceptional case, however, as most Cleveland FM stations run no more than 50kW at most.) The further away from the station the listener was located, the more difficult it became to get a decent signal (this was made worse with the advent of stereo multiplex FM in the early sixties, as stereo signals are weaker than monophonic FM signals of the same power level, again becoming weaker the further away from the transmitter the listener was). It was not uncommon in the 1950s-'60s for serious FM listeners to have large FM antennas, sometimes on rotators, on the roof of their homes or in the attic, often on the same mast as the television antenna.
BTW, I think it is a darn shame that most cable television service providers no longer provide FM stereo stations as they once did. There are areas of this country which get poor or no FM reception, either because of sheer distance from major cities or due to terrain features such as mountains, etc. that block the area from receiving much of anything (if the small town/city in question has no local or nearby FM stations). When the cable companies carried FM service, it brought city-grade FM signals to these areas, but in these days of most if not all cable operators providing no FM service (stereo or otherwise), these folks in small towns blocked from big-city FM stations will (and often do) have little or nothing much to listen to unless they forgo FM for such services as Internet radio. The latter can be an alternative to FM, but there is a catch: the fidelity of these services is only as good as the sound card in your computer and the quality of the speakers, either the ones that came with the system or the speakers in your stereo system (if you feed your computer's audio output through your system's amplifier).
But also, having 4 separate conductors, separated by their insulation, *may* act like having four elements even though they're tied together. I dunno if it'd be significant or not, I'm not an expert either... I have seen that multi-turn loops are sized differently.
