Apache Redirect without including the root of the document in the rewrite rule

I have this rule of thumb:

RewriteRule ^ (. *) / Amp / $ https://somedomain.com/$1?amp=1 [QSA,R=301,NC,NE,L]

To redirect "https://somedomain.com/register/amp/" to https://somedomain.com/register?amp=1

And it works well, but I would like, that the URL in the browser does not change, so he will load the registry? Amp = 1, but in the browser always show / record / amp /

To get this behavior, I try to edit for:

RewriteRule ^ (. *) / Amp / $ ./app.php/$1?amp=1 [QSA,R=301,NC,NE,L]

But then he redirects to https://somedomain.com/home/user/public_html/register?amp=1

So, it's add the root of the document wrongly and I do not know how to modify the rule to achieve it.