$ cat /etc/portage/package.mask
=x11-base/xorg-server-1.0.1-r2

$ sudo emerge -va =x11-base/xorg-server-1.0.1-r2

These are the packages that I would merge, in order:

Calculating dependencies ...done!
[ebuild     U ] x11-base/xorg-server-1.0.1-r2 [1.0.1-r1] USE="dri ipv6 xprint -debug% -minimal" 0 kB 

Total size of downloads: 0 kB

Do you want me to merge these packages? [Yes/No]