How to target multiple countries from single site without using sub domain or folder?

Google has info on hreflang.

• Use hreflang for language and regional URLs

Yes you can.

Pretty much all you have to do is add the relevant hreflang tags to the head section of each webpage in a language set, don't forget the default one.

Be aware get your hreflang tags wrong and Google might ignore them all. Recently reviewed a site Language Teaching Resources - Languagenut US with the sort of setup you want to achieve.

My SEO review : Languagenut SEO Review

They'd made errors in their hreflang tags, looks like whoever setup the hreflang tags assumed if a WordPress Post existed it would exist in all 60+ languages (they didn't) and added 60+ hreflang tags code to each Post with format "example.com/countrycode/post-name/".

Even when there was the same content in different languages they'd used different Post Names ("post-name" part of URL above), so pretty much none of the hreflang tags were valid. Think they've removed the code now, they have no hreflang tags so have a duplicate content issue instead: maybe they'd submitted an XML sitemap with the language sections to Google which is a better solution for a site with a lot of language sections.

Anyways, this is the code you want for every webpage in a set if you have three languages (US, UK and DE):

This code goes in the head of all three webpages. Obviously replacing the -URL bit with the relevant URLs.

If you add or remove a webpage from the set, all of the webpages in the set have to be edited. If we added another language we'd add a fourth hreflang tag line above and add it to the four webpages. If we deleted a webpage, the remaining webpages have to be edited to remove the deleted webpages hreflang tag.

Managing this for a site with a few languages is challenging, manging a site with dozens of languages is a nightmare: consider an XMl sitemap.

David