Experiment to figure out how NSDictionaryOfVariableBindings works, and try to make a more flexible version. This version strips underscores and supports self.* variables, but I'm sure there is a better way to do it.

ZWDictionaryOfVariableBindings.m

#import <Foundation/Foundation.h>

// Experimental improvement to NSDictionaryOfVariableBindings where keys are simplified to remove underscores and "self." prefixes
// so you can use the simple version within the VFL string
//
// Example:
//
// [NSLayoutConstraint constraintsWithVisualFormat:@"|-[_foo]-[self.bar]-[baz]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(_foo, self.bar, baz)];
// -> this doesn't work, gives an error about "self."
// 
// [NSLayoutConstraint constraintsWithVisualFormat:@"|-[foo]-[bar]-[baz]" options:0 metrics:nil views:ZWDictionaryOfVariableBindings(_foo, self.bar, baz)];

#define ZWDictionaryOfVariableBindings(...) _ZWDictionaryOfVariableBindings(@"" #__VA_ARGS__, __VA_ARGS__, nil)
NSDictionary * _ZWDictionaryOfVariableBindings(NSString *commaSeparatedKeysString, id firstValue, ...) {
    va_list args;
    va_start(args, firstValue);

    NSMutableDictionary *dict = [[NSMutableDictionary alloc] init];
    NSArray *keys = [commaSeparatedKeysString componentsSeparatedByString:@", "];
    NSInteger idx = 0;
    
    for (id arg = firstValue; arg != nil; arg = va_arg(args, id)) {
        NSString *key = [[keys[idx] stringByReplacingOccurrencesOfString:@"_" withString:@""] stringByReplacingOccurrencesOfString:@"self." withString:@""];
        NSLog(@"variable: %@, key: %@, value: %@", keys[idx], key, arg);
        dict[key] = arg;
        idx++;
    }
    
    va_end(args);
    
    return dict;
}

int main(int argc, char *argv[]) {
    NSString *_foo = @"__foo__";
    NSString *bar_ = @"__bar__";
    NSString *baz = @"__baz__";
    
    NSDictionary *dict = ZWDictionaryOfVariableBindings(_foo, bar_, baz);
    NSLog(@"dictionary: %@", dict);
}

// clang -framework Foundation ZWDictionaryOfVariableBindings.m -o test && ./test

// Output:
//    2014-04-16 15:48:58.686 ZWDictionaryOfVariableBindings[66046:507] variable: _foo, key: foo, value: __foo__
//    2014-04-16 15:48:58.688 ZWDictionaryOfVariableBindings[66046:507] variable: bar_, key: bar, value: __bar__
//    2014-04-16 15:48:58.688 ZWDictionaryOfVariableBindings[66046:507] variable: baz, key: baz, value: __baz__
//    2014-04-16 15:48:58.689 ZWDictionaryOfVariableBindings[66046:507] dictionary: {
//        bar = "__bar__";
//        baz = "__baz__";
//        foo = "__foo__";
//    }

This was a quick hack, I wouldn't actually use this without some more tests

For anyone curious, the macro/function setup is exactly how NSDictionaryOfVariableBindings works, so I just copied the same method:

// From NSLayoutConstraint.h

/* This macro is a helper for making view dictionaries for +constraintsWithVisualFormat:options:metrics:views:.  
 NSDictionaryOfVariableBindings(v1, v2, v3) is equivalent to [NSDictionary dictionaryWithObjectsAndKeys:v1, @"v1", v2, @"v2", v3, @"v3", nil];
 */
#define NSDictionaryOfVariableBindings(...) _NSDictionaryOfVariableBindings(@"" # __VA_ARGS__, __VA_ARGS__, nil)
UIKIT_EXTERN NSDictionary *_NSDictionaryOfVariableBindings(NSString *commaSeparatedKeysString, id firstValue, ...) NS_AVAILABLE_IOS(6_0); // not for direct use

This is great, I didn't know #VAR_ARGS could get the inputs as strings like that! Thank you for sharing.