Instead of sea-foam you could use just water drawn through the vacuum line. This would have the effect of steam cleaning the combustion chamber and piston tops.

In extremely cold weather, I have had to use kerosene to dilute or thin 30W crankcase engine oil (didn't get changed to winter grade). This dilution also loosens sludge/crud build up. However, I wouldn't leave it in for very long. Large amounts of raw fuel, even kerosene in oil tends to wash cylinder walls of lubrication.