That's what I've done for my 'new' n770.
I bought cheapest Kingston's MicroSD card which came with two converters - MicroSD-MiniSD (needed for my n810) and 'spare' MicroSD-SD.
You can say that I should simply buy another RS-MMC 2GB card and forget all the trouble but - I needed this converter for n810 and... this was 1$ cheaper solution

First - I dissassembled MicroSD-SD converter - it's easy with sharp knife since it's not glued for this specific type.
Once You open one - You can see connectors fixed with little plastic bar.
Connectors are delicate so It's not good idea to throw away supporting plate (on the left).


The idea was to cut space for microsd card in this supporting part.
On photo below You can see connectors glued with UHU to cut supporting plate (glue between support and connector's plastic bar).


Below You can see how it looks from the other side.


Contacts need to be straightened and bent to the 'other side'.


Below it's a test - pins not bent to their final position.
As You can see - card placement is good enough.


Then - when making them more twisted - card locks itself in.
They are elastic spring contact so it's easy to push the card downward at it's end to get good connection at all contacts.


Now to position the card I cut a part of plastic from card's blister.
It's bit too thick though.


Now - glue this cover.


And for the final touch - isolate connectors using some transparent adhesive tape.



Voila.
I'm using Fanoush's high speed sdhc enabled kernel so any available MicroSD card will do.
It's bit thicker than RSMMC card - mainly because of my transparent plastic cover.
I was able to place it in n770's slot with no problem from the first time.
Of'course one can say that it's not elegant and doesn't survive many plugin cycles but c'mon - it's cheap, fast and with nothing to loose as long as You dont short connector pins.
Feel free to modify.