I'm not experienced with Oestrogel but I know quite a bit about the nausea as I suffered very badly. I believe it is caused by the oestrogen surges and I used the combined contraceptive pill to over-ride my cycle as much as possible in order for them to stop. I suspect the same can be achieved with Oestrogel.
I think the surges are caused by the brain registering a fall in oestrogen which then causes it to panic and push the ovaries to throw out more oestrogen causing nausea in some women. If you have enough oestrogen from your gel then it may stop the surges so having more would seem to be the best option in my opinion. I don't think the timing of when you use the gel is so important in this case, as you want to build up enough oestrogen for the natural falls not to register. My nausea was always better by the evening and I think this is due to adrenaline levels naturally falling at that time, which tie in with the whole process of over-stimulation.
It took me about 8 days for the nausea to stop with the pill and, at first, made the nausea much worse as it was initially just adding to the problem until the levels had built up. So you could try either option, more pumps to control the cycle and calm the brain from shunting more out, or 1 pump may be enough for what you need but not too much to add to the natural oestrogen surges to cause nausea.