Set your rules as follows:
.htaccess at DOCUMENT_ROOT
RewriteEngine on
RewriteBase /
RewriteRule (.*) mycakeapp/$1 [L]
.htaccess in DOCUMENT_ROOT / mycakeapp
RewriteEngine on
RewriteBase /mycakeapp/
RewriteRule (.*) app/webroot/$1 [L]
.htaccess DOCUMENT_ROOT/mycakeapp/app
RewriteEngine on
RewriteBase /mycakeapp/app/
RewriteRule (.*) webroot/$1 [L]
.htaccess DOCUMENT_ROOT/mycakeapp/app/webroot
RewriteEngine On
RewriteBase /mycakeapp/app/webroot/
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.php [L]