I am currently trying to get sage to use a system wide singular.
This is provided by sage-core-4.5.1-r1 and sage-4.5.1-r1 which
are masked. You have to use the latest version of the singular
ebuild with the libsingular use flag. If you don't have a folder
/usr/include/singular merge singular again as we added some
headers that are needed to compile sage-core this week end.
It currently segfault on my machine - you've been warned - but
I am working to fix it with Thomas Khale.
It is uncertain at the moment if sage-4.5.2 (from upstream) will
use this version of singular or not - it was planned for 4.5 then 4.5.1
and someone else upstream experience segfaults with it -
on Solaris. So upstream move may be delayed again.
However we want to get rid of sage-singular ASAP.