You can put some white embroidered curtains in the windows. Greek houses always have curtains. The most traditional ones have a special technique called "kofto". It always reminds me of home..
http://www.kendimata.gr/index.php?cPath=23_53
Or some greek little rags we use here, called kourelou. It is very greek!
http://www.flickr.com/photos/86857387@N00/2785007651/
http://www.galaxidigreece.com/greekcarpet/003-09/index.html (don't pay much for a kourelou).
Even the fashion designer Sofia Kokosalaki was inspired by the kourelou technique!
What about shag rugs (flokati)? http://www.flokati.com/
They're ideal for winter, traditionaly made from wool but I suggest cotton because it is easier to clean.
A pot with a basil plant is usually found in many greek homes, and it will definitely bring back memories of summertime in a quiet village.. http://www.greenhousegrower.com/articles/image/05%20edibles/Basil%20Aristotle%20big.jpg
Or you can plant some basil seeds in a red ceramic pot without telling him what's in, and you will watch the plant growing! What a nice surprise. http://www.gardenguides.com/2712-basil-greek-mini-seeds-bulbs.html
If he is coming from the islands, some decoration using seashells would be nice. I-don't-know-how-this-is-called--> http://2.bp.blogspot.com/_5S-vBmj8wfY/SKF_GnscrGI/AAAAAAAAAfI/jG8ny7B-GGo/s320-R/P7230185.jpg
If he is coming from mountainous areas, rustic ceramic plates would be the norm.
What about some wooden kitchenware? http://greekfood.about.com/od/greekcookingbasics/tp/kitchessentials.htm
Only for cooking, not for eating!
Is he religious? you could place an orthodox icon somewhere. http://www.religiousmall.com/prs_wooden_icons.html
I mean, Greeks celebrate namedays. http://www.namedays.gr/index_uk.php
If his named is Nick (Nikos) he celebrates at December 6th, and you could give him a Saint Nikolaos icon.
What about backgammon (tavli)? All Greek homes have a backgammon board! Even if they don't play backgammon.
Isn't that enough?