If the turbo gaskets have not had heat applied to them, you should not have any issues with reusing them. Once they are used on a running engine the heat and related expansion of metals will apply more pressure to the gasket than the applied bolt torque from assembly. I had a similar issue during one of my builds and experienced no gasket issues. As far as cutting the oil return hard line, it does sound feasible as the low pressure turbo does have a hose segment on the return. There may be an issue with heat proximity on the high pressure turbo oil return but I don't remember the actual routing.

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2012 X5d fully deleted
SPD Custon Tune,
6r80 Stage 2 trans clutches,
Colt cams, hybrid turbos,
ported head and manifold,
VRSF intercooler,
Dual HPFP's, 100% over injectors,