Prefixing array keys with a string (:) in PHP

Question

Quick one; I know a solution, but I'm looking for something more elegant if it exists.

I'm using PDO for prepeared statements:

$sql = "INSERT INTO my_table (foo, bar, baz) VALUES (:foo, :bar, :baz)";

$source->execute($sql, array(
    ':foo' => $foo,
    ':bar' => $bar,
    ':baz' => $baz,
));

This is fine, but I want to pass in a previously created array, however the keys contained aren't prefixed by the colon (:), and I figure there must be an elegant way to take:

$array = array(
    'foo' => 'some',
    'bar' => 'random',
    'baz' => 'value',
);

And translate it into:

$array = array(
    ':foo' => 'some',
    ':bar' => 'random',
    ':baz' => 'value',
);

Without doing:

$temp = array();
foreach($array as $key => $value){
    $temp[':' . $key] = $value;
}
$array = $temp;

I've browsed the PHP docs, but I can't find a function (or sequence of) that suits the purpose.

Any ideas?

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Addendum

Leaving the accepted answer, but +1 @chim for his clever 1-liner; solves the X in my XY problem. Reformatted solution:

$format = ':%s';
$values = array_flip(array_map(function ($key) use($format) {
    return sprintf($format, $key);
}, array_flip($values)));

Wrapped in a function, perhaps array_keys_format(array $array, $format)

Answer 1

$source->execute($sql, array(
    'foo' => $foo,
    'bar' => $bar,
    'baz' => $baz
));

This is presuming the above calls PDOStatement::execute() under the hood, with the above array as its argument.¹

:)

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^{1) Tested with version 5.2.17 and 5.3.8 here, and working as expected.}