Passenger side turbo has challenges being worked on even when the engine is out of the car because of proximity to the front differential housing. You 'can' perform work on the oil lines without entirely removing the power plant yes - but ONLY the two top lines. You cannot perform work on the lower oil lines without removing the turbos entirely as access to the two 4mm allen head bolts are sandwiched between the underside of the turbo housing and the bell housing of the transmission.... For the top lines you can gain access by lowering the cradle, but depending on how small your hands are, how good your tools are, and how 'lucky' you are to have bolts come loose with limited access to properly torque on and off, you will need to lower the cradle quite a bit.
Ramifications of this include the requirement to then decouple the oil cooler lines, tranny cooler lines, rad hoses, upper and lower intercooler hoses, power steering pump hoses, and even the air conditioning hoses. These all have insufficient slack to drop the cradle enough to get your hands up on either side of the chassis to where the oil lines are (fasteners located on the top of the turbo). You also need to unbole the engine snubber bushing and also decouple the lower control arms from the cradle as the DRC lines don't have sufficient slack either (exception to this is if you have aftermarket dampers in which case you can simply unbolt the top mount of the strut from the pillar mount).
Finally, you need to unhook the exhaust, and also the drive shaft (or at a minimum the bracket for the centre support bearing) because you simply can't put that much strain on the back part of the powerplant and there is insufficient room within the engine compartment to lower things on enough of an 'angle' while either the front or rear remains bolted up. Only good news here is that you don't need to decouple the starter wiring harness or the transmission wiring harness as each has sufficient slack once you snip a few zip ties holding each to the chassis. Complicating matters are the fact that almost all cars will still have their SAI system still in place making it more difficult from an access perspective to get your hands in to work between the back of the heads and the firewall. You can also access from the sides down below. The oil line bolts are sandwiched in between the header and the housing of the turbo. Take a look for yourself at the photos below. Bottomline, engine should be lowered equally front and reat and by the time you do all the work above necessary to access in the first instance, you're only a short ways from the finish line making it more reasonable to remove the entire hulk and service this item and any others requiring attention....
Based upon the fact that you cite there being a leaking 'gasket', I have to presume it's one of the braided lines leaving that runs from the bottom of the turbo housing and dumping back in to the oil pan. The top lines are sealed in the same manner as gas lines with a pair of soft metal compression washers. Good luck with things.
Pics showing what you can access with cradle lowered and powerplant still "in" chassis...
Pics of what you access with engine out. Again, biggest problem is accessing fasteners that bolt bottom return line on to the turbo housing. If it wasn't a 'significant' leak, I might be inclined to let it leak and only repair things until you MUST remove the powerplant for something else that is impossible to service with the powerplant in situ. You did say significant though.....