There are some electronics in the shifter assembly. You would have to open it all up to make sure the spray goes just into the cable.

The bicycle industry sells clamp on tools that let you spray lube down a cable - the sizes are slightly different but that might work to get lube further onto your cable from underneath. Amazon has several. Bike shops probably stock them.

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David.X5
2001 X5 4.4i Sport
SOLD! at 160k miles