Smarter way to do a combinator attack with different rules for -j/-k?

[voideater]

I want to try a combinator attack where I combine two dictionaries with a '@' between the words in the dictionaries and add four digits to the end of the combined words, e.g. if

dict1

Code:

cat
dog
car

dict2:

Code:

coke
sprite
fanta

I want the output to be (YYYY for some year):

Code:

cat@cokeYYYY
cat@spriteYYYY
.
.
car@fantaYYYY

I've tried using -a 1 with -j '$@' -k '@YYYY', but seems like this only works if -j/-k adds the same amount of characters (e.g. as in the example at https://hashcat.net/wiki/doku.php?id=combinator_attack) - unless I'm doing it completely wrong of course.

I could append '@' to all the words in dict1 and then combine the modified dict1 with dict2 using combinator before running the rule attack, but before I do that I wonder if there's an easier way? Doing it this way could lead to a quite large combined dictionary that'd take up quite some disk space if dict1 and dict2 both contain a decent amount of words.

Even better if it's possible to do -k '$?d $?d $?d $?d' so I could try appending all four-digit combinations to word1@word2 without having to manually specify YYYY for each attack I do. If that's asking for too much I'll just do the attack in a loop where YYYY is incremented for each iteration.