It will not be comfortable ----- they (24" cruisers) are too small for an average size adult to actually ride ---- you would have to source an XL seatpost and reinforce it somehow to keep it from collapsing backwards -- keep in mind these little bikes are only made to be ridden for 45 seconds at a time and the seat is usually only on there for decoration when in an actual BMX race

Mine pictured is a 26" wheeled machine and I had to epoxy a wooden dowel inside the seatpost to keep them from folding backwards when I had it extended for actual riding outside of a BMX track