I know one good way to do it.
1) Give yourself a cart that has no ZSC entry so that it is invisible
2) Change the value in LIST_PAT.STB that defines the character animation (column 41) It is normally set to 261 which gives you a seated position but a bit of experimentation here can come up with all kinds of fun results
Once you get this right, you will appear to be floating as you drive your cart