my @param = $q->param();
@input{@param} = map $q->param($_), @param;
[download]

I couldn't be bothered to Benchmark it but I suspect this is going to be the most efficient or at least a very competitive variant, especially so if the number of parameters is substantial.

Update: Or maybe this:

my @param = $q->param();
@input{@param}=();
$input{$_} = $q->param($_) for @param;
[download]

Finally, this leads us to another variation which I like best:

@input{$q->param()}=();
$input{$_} = $q->param($_) for keys %input;
[download]

Between the latter two, I'm not sure which one will perform better.

Makeshifts last the longest.