The motorwayactually directly ramps into Viale Guiseppe Cattori in the city centre Paradiso. Theorectically it is possible to hitch from there but the traffic may divert before the slipway is lifted up. There is a 4-way roundabout at the end of Via Pian Scairolo. The 1st exit ramps onto A2 and there is a slipway aside too. Stand on the kerb inbetween and face the traffic with a sign. It is right under the road lamp, so it is possible to hitch at night there.
North towards Bellinzona
The main problam in hitchhiking north from Lugano is the fact that until Bellinzona (about 25km) there is no petrol station or a good stop on the highway. The two option you do have is either to go south of Lugano, where there is a big gas station on the highway, or try to hitch on a side road to Bellinzona. It is legal to hitchhike on a regular road, and many people do stop, but a lot of them just few KM each time. Anyway once you are in Bellinzona there is a petrol station going north, as on the map. It's possible to reach it by foot without going on to the highway, and from it you can reach Zurich, Luzern, Basel going on and also Austria when going on .