i've got a powershell script i use to update a lightspeed nuget package which I have created and host locally.
msi uninstall prev LS version
create nuget package (have done this bit) - i just bump the package version number and nuget pack the LS files into my local nuget store
then it's easy to update LS to the latest nightly build in all my solutions.
fwiw, and while you're thinking about nuget support for v5/nightly builds, i noticed this - might have some useful ideas for you: http://aspnetwebstack.codeplex.com/discussions/353867 if you were to do something similar, it would be great if you did implement the pre-release versioning for assemblies.
and if you're able to create an secure nuget feed (for those who have purchased the source code license), would be triple awesome if you could provide non-obfuscated nightly build nuget packages.
those of us who are using nightly builds will come across LS bugs sooner than others - if we have the full LS stack trace it can make it much easier for us to generate a repro for you (without our having to recompile LS from source or try to walk the LS stacktrace via method signatures only - not fun!!).