Xander - a common nickname for Alexander. The x is pronounced as a z, but it still has the problem with the American a.
Sunder - Not as common, but it's a name Americans might have heard and in my opinion is closer to the Dutch Sander than "sender".
San Der - For the large percentage of Americans who are familiar with Spanish pronunciation, you might have luck with this spelling, but those Americans probably aren't the ones who mispronounce the Dutch version.
"Like Shaun Der, but with an S instead of an Sh on the front" - The way I explain the Hungarian variant Sandór to Americans is "like Shaun Door".
For my own name, Ambroos (Dutch as well), I've yet to find a good English rhyming word. I've just settled with telling people to pronounce it as Ambrose. It's better than people turning it into Am-bruce. For TTS I sometimes use Ahmbrohs.