:[line]pu[t] [x] Put the text [from register x] after [line] (default
current line). This always works |linewise|, thus
this command can be used to put a yanked block as
new lines.
:[line]pu[t]! [x] Put the text [from register x] before [line]
(default current line).
:nmap <F4> :call append(line('.'), @")<CR>
" This one may be a little better (strip the ending new-line before pasting)
:nmap <F4> :call append(line('.'), substitute(@", '\n$', '', ''))<CR>
:help let-register
:help :call
:help append()
:help line()
:help nmap