Dual-boot with Windows 10

I've just acquired a refurbed E575 with a fresh Win10 install on it,
which I'm intending to dual-boot with Debian.

In the past I've just 'shrunk' Windows and created an extended /sda4
partition with several logical partitions in it (for OS and data)

However, in this laptop Windows has been a bit greedy thus: 
(according to Gparted):
/dev/sda1	ntfs	Recovery	499MiB	hidden
/dev/sda2	fat32			100MiB	boot
/dev/sda3	Unknown			16MiB	msftres
/dev/sda4	ntfs			465GiB

... so the bulk of Windoze is in /dev/sda4 so I can't create an
extended partition there without blowing Windows away.   Which I will
do if I have to, but is there an easy way around this?

Any advice gratefully received.

Chris Rodliffe
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