Sure… you just need to compile your lambda and then invoke it…
object input = 4;
var compiledLambda = lambda.Compile();
var result = compiledLambda.DynamicInvoke(input);
Styxxy brings up an excellent point… You would be better served by letting the compiler help you out. Note with a compiled expression as in the code below input and result are both strongly typed.
var input = 4;
var compiledExpression = exTyped.Compile();
var result = compiledExpression(input);