I need to fetch an outsider from about 20km far away and I want to use my bicycles. I have used roller skaters with a bicycle to fetch my friend, I let my friend to use the bike while I will stuck to the back at the destination -- it is very cool and convenient (light weight) when you know your friend but doing it with unknown outsider is not be the best option because it requires trust between the participants. My next best option is to use my foldable bike stuck to my back-bag and my diamond-framed bike but the foldable bike weighs about 10 kg. I have been considering a number of options such as tandem, an unicycle and side-cargo thing but many options tend to be expensive. I don't want to use rack based sitting approach because it would damage the rack.
How do you fetch your friends or outsiders over long distances when you need to carry the transportation equipments to one-direction alone and then allow the friend/outsider to use the equipments to move to the other direction with you?
If you are suggesting a thing such as tandem that may be too expensive, let me know whether you could hack your standard bike such as diamond framed bike to a tandem so that I could get it cheaper.