I just ported it.
and upload to autobuilder in Extras-devel.
I think it will be available in an hour.
Package is optified. I didn't make a lot of testing. If it will not work post here.....

You can check status of porting here: http://maemo.org/packages/view/p7zip/
It will have 2 packages p7zip and p7zip-full. On root will be installed around 10kb other will be in /home/opt

Edit: It was build and soon will be in repository
Edit: It is now in Extras-devel. For getting help type 7zr in x-term