I'm still in the middle of building packages for our clients for the packages that aren't normally distributed for windows to make upgrading to PostgreSQL 9.4 smooth. One of those is PL/V8 which we use for some custom functions.
I had mentioned how I build PL/V8 for PostgreSQL windows, and the instructions are a bit out of date., but I put more up to date instructions on my gist page. I tend to use gist a lot as a public scrap book with hopes someone else can learn from my toils and save them some trouble. At some point I should probably get more organized with my scrapbooks.
I've listed below PL/V8 binaries I built for PostgreSQL 9.4 for windows 64-bit and 32-bit. These I tested with EDB PostgreSQL 9.4 windows installs and seem to work fine. These were built with latest 1.4 branch (a little after 1.4.2 to grab the extra 9.4 fixes) of PL/V8.