beamer table of content: put only the current section and subsection at the top of the slide

I'm writing a rather long beamer, with many sections. The toc with sections fit in a single slide, but when, at each section, I show the subsections, it gets too long and we cannot see it. I would like , at each beginning of section/subsection, to display the toc for that section only, aligned at the top. Currently, when getting to section 4, I get, where === represents the slide limit:

 ============ 1. Section1 2. Section2 3. Section3 4. Section4 4.1 Subsection 41 =================== 4.2 Subsection 42 (so it gets out of the slide) 5. Section5 

I want to have:

========== 4. Section4 (aligned at the top of the slide !) 4.1 Subsection 41 4.2 Subsection 42 (free space here) ======== 

Even if i use sectionstyle=show/hide, subsectionstyle=show/shaded/hide , the position of the section is "remembered". Thanks!