Have had one since 1994 and visited WG's on a fairly regular basis since. The majority of times I've not mentioned it beforehand and it hasn't been an issue.
Can think of only one occasion when the WG refused to go through with the punt. To be honest it was a WG I'd picked in haste and saved me £50 that I would have regretted spending.
Reactions have varied from never even been mentioned (probably most common reaction), "what's that", "what's that for", "will I hurt you" - has never happened (my preference is for the slimmer girls, but have seen some hefty girls). Some have mentioned that they've seen other clients in the same position.
It goes without saying that I always make sure it's a fresh appliance and have a bath or shower beforehand.
In short shouldn't be a problem for you, but can understand the concern.