I would put this in quotation marks, with a short explanation in brackets.

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26 Nov 2007 – Human Resources has had a number of questions about the status of ... 31, which are known as "sandwich" days because they fall between a ...

1) post-holiday day off
Es una posibilidad, pero se pierde la idea de "sandwich".
Ejemplos:

Good Things Come to Those Who Write: Obligatory Christmas Post
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4 days ago – ... three family events into roughly twenty-four hours, it did occur to me that I would also be very grateful for a post-holiday day off to recuperate.

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15 Apr 2009 – Election Day, National Holiday? Dec 9, 2007 6:47 PM. Why is election day not a national holiday? NJ workers lose post-holiday day off. Nov 17 ...

En el siguiente no es "day off", sino "take off", pero ilustra igualmente la idea.
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26 May 2008 – ... but eventually failed to do so without the support from local players, many of whom had taken the post-holiday day off. Activity should liven up ...

2) "bridge day (off)"

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snowplow, don't forget Thursday was a bank holiday for most of the continent and an awful lot of people take a bridge day on the Friday and many companies do ...

A mí me gusta más el término "bridge days (off)", entre comillas, como se hace en el siguiente artículo de Wikipedia sobre "Long holidays": http://en.wikipedia.org/wiki/Long_weekend.
http://es.wikipedia.org/wiki/Puente_festivo.

Otro ejemplo, pero con comillas:
how can I assign a special day type to a worksc... | SCN
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20 Apr 2010 – I need to mark a Friday as a "bridge day off", Thursday being a holiday. I am defining the Friday as a special day type 3. How are special day ...

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2 May 2008 – Everyone in their right state of mind would take such a Bridge Day off to have a short 4-day holiday, but of course the fact that people in their ...

3) "long weekend"
Una tercera posibilidad, si el contexto lingüístico lo permite, es usar el término "long weekwend" (http://nextlongweekend.com/).

Mira también: http://www.proz.com/kudoz/german_to_english/human_resources/...

is how I'd put it, a combination of two of Alejandro's answers. These days are not as common in English as in other languages so I think the context of "long weekend" is required

you could also say "a four-day bridge weekend" as in the link below but I think "long weekend with bridge days /extra days taken (as holidays) is better

http://en.wikipedia.org/wiki/Long_weekend

Worldwide Public Holidays News: July 2007
qppstudio-public-holidays-news.blogspot.com/2007_07_01_archive....
31 Jul 2007 – As expected, we now have the first announcement from civil servants that the **in-between day** will be taken as a bridge public holiday.

MIXED SALAD RETURNS THIS ST PATRICKS WEEKEND!! 2 FLOORS. OVER 20 ...
www.bodytonicmusic.com/forum/8152/topic/view/ - Ireland
... Thomas St every bank holiday Sunday, Mixed Salad was also famous for its ... all a day to recover before the dreaded **in between day** of work on the Monday!

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Note added at 4 horas (2012-12-30 19:49:40 GMT)
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Friday was the **in between day**; the day after the holiday and the day before another holiday 8th December which celebrates the Immaculate Conception. Some people have all three days off which is called a “Puente” (bridge).