How can I handicap Ticket To Ride: USA, without seeming patronizing?
Some actions you can take, in increasing order of difficulty it will impose:


Don't aim for the Longest Route.
Don't draw from the visible options. This will reduce the 'skill' you can exercise, making your plays more dependent on luck. 
Don't use wild Cards to fill out a color set. Makes it harder to get the longer routes. Knowing that they may gather in your hand, you can still use them as a full set to claim a route.
Don't use wild cards at all. 
Increase the number of trains you have to collect to claim the smaller routes. Instead of 1, 2, 3, 4, 5, and 6, use 2, 3, 4, 5, 6, and 6. This will drastically slow your ability to claim routes. Don't actually play the extra card, just collect them.