Euonymus seeds are quite oily (on the outside). You may remember that they were slippery when handling them. The usual procedure is wash them in a bit of soap and water first, as it is believed this coating can inhibit germination. Be sure to rinse thoroughly afterwards.
Cold stratification ONLY occurs with seeds that have already imbibed water. Dry seed given a cold treatment as was the case when you collected them, is simply seed storage. It is not cold stratification. Euonymus species seed in general are very erratic germinators and usually require at least one cold cycle, or at least one warm then cold cycle to germinate.
So if they are still in water, I would wash them with a drop of soap (even the swelled ones), plant them, and start you cold treatment in the fridge. Around mid March, I would put them outside in the shade, enclosed in a clear bag, to experience varying temps (deep freezing is fine), and let them germinate at the temperature that they want. Heating pads are rarely a good thing for seeds of temperate woody plants. Some woody plant seeds will want to germinate at 50F or even 40F, and won't germinate at 70+F.
