I found that by default lease file is disabled and there is no way to enable it using USE flags. Could these patches be added to main portage tree?
Created attachment 307355 [details, diff] ebuild patch
Created attachment 307357 [details, diff] metadata.xml patch
Added in -r1 , enabled by default, so no useflag (there is no sense in disabling it at compile time, people can just comment it out in their config file) :)