According to TIS you can get the fuel pump out through the service portal next to the propshaft.
It says that you only have to remove the exhaust&heat shielding.
I don't know if there's an opening on top of the tank. (don't think so; TIS says the fuel pump assembly goes through that hole)
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Z4 3.0i | ESS TS2+ supercharger | Quaife ATB LSD | Brembo/BMW performance BBK front/rear | Schrick FI cams | Schmiedmann headers+cats | Powerflex/strongflex PU bushings | Vibra-technics engine mounts | H&R anti rollbars | KW V3 coilovers/KW camber plates | Sachs race engineering clutch | tons of custom sh#t
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