Be advised this is probably WAY more than you want to know but...
Heelys are along the same lines but ...not, if you know what I mean. When these first came out, people asked for them for their kids but they had the kind your friend owned in mind and needed to be persuaded that they were NOT looking for the sneaker skate. Those had front wheels and all of the wheels popped in and out of the soles as you described.
Heelys come with a rubber plug in the heel. You use a special tool (or a freakin' screwdriver) to pop out the plug. The wheels then snap into the HEELS only. You need the tool to pop them out and put the plugs back in.
The kids don't skate on them as with regular skates. The walk quickly and then rock slightly back on their heels and glide on the wheels in the heels, one foot in front of the other.
Hence the name Heelys. It looks strange but they are huge on the east coast. Don't know about the rest of the country.
BTW...shoe skates (Quad Skates) are making a comeback.
People are shelling out 60 bucks to have their own skates for the rinks ever since the movie "RollBounce". What goes around, comes around.