there is probably a better way to do this, but I don't feel like messing with load order or the like.
You can edit rails.vim and add one line. It works as I would expect in my tests.
" Initialization {{{1
augroup railsPluginDetect
autocmd!
autocmd BufNewFile,BufRead * call s:Detect(expand("<afile>:p"))
autocmd VimEnter * if expand("<amatch>") == "" && !exists("b:rails_root") | call s:Detect(getcwd()) | endif | if exists("b:rails_root") | silent doau User BufEnterRails | endif
autocmd FileType netrw if !exists("b:rails_root") | call s:Detect(expand("<afile>:p")) | endif | if exists("b:rails_root") | silent doau User BufEnterRails | endif
autocmd BufEnter * if exists("b:rails_root")|silent doau User BufEnterRails|endif
autocmd BufLeave * if exists("b:rails_root")|silent doau User BufLeaveRails|endif
autocmd Syntax railslog if s:autoload()|call rails#log_syntax()|endif
" Add this line here
autocmd VimEnter * if expand("<amatch>") == "" && !exists("b:rails_root") | call s:Detect(getcwd()) | endif | if exists("b:rails_root") | Rproject .project | endif
" ^ this one
augroup END