Hi Kazj,
Strangely enough, blowing a balloon up with his nose is something I was told for my sons too. It helps, I guess, if your child can manage it but four may be a bit young. Depends on the child of course.
Two of my sons were diagnosed with Glue ear, one so bad, under the age of two, his speech deteriorated (which is how I realised there WAS such a problem) and I had to take him for speech therapy to help regain his speech. Awful. He is now 17, 6ft 1 or 2 and strong as an ox. He was also badly asthmatic as a young child.
It can be a problem with little ones as when they're small the Eustacian/eustachian? tubes are small and more horizontal yet as the child grows they apparently grow less horizontal and fluid can drain away more easily. Correct me if I'm wrong, you anatomy studiers or medical people, but that's what the ENT guy said and it's stuck in my mind forever more!

Looking back and seeing what I did to alleviate or prevent the problem occuring, I would suggest the following:
Get him off dairy. Sorry if that's hard to do, but I realised this was a major factor with my kids. We switched to soy and rice milks.
Build up his health and general immunity so he gets less colds and sniffles. Garlic, vitamin C, echinaccea - the list is long! Eat wholesome, whole foods and cut out any junk and processed stuff. Take this as an opportunity to get him and his whole family healthy.
Visit a naturopth and/or homeopath and see what they suggest.
Investigate ear candling. The people in the line above can probably advise on how this can assist. I thought this was Very Strange twenty years ago
along with moxa burning and Other Wierd Things but it seems to work.
Familiarise yourself with Tissue Salts. We use Nat Mur and Kali Mur for any sniffles (but don't need them much any more). Seems to bring things out very quickly and fast tracks you to recovery. Used to be in tablet form which you dissolved under your tongue but now in oral spray as well which is great for littlies. Available in health food stores. We use Martin & Pleasance.
My elderly mother swears by Vicks for a lot of things including clearing the nasal passages. I resisted for eons but am beginning to think she's right. I also used to put a few drops of a certain essential oil in a bowl of hot water and had my sons bend over that with a towel all around, breathing in and out steadily for a few minutes. An old remedy which will help, although I cannot remember what oil I used now!
:confused:
All the best. Let us know how you go...
Ree