In general it is not a good idea to do isolated kanji > keyword tests. Particularly so if you use the Spaced Repetition System, as you would end up with twice the amount of reviews at the cost of really focusing on completing RTK which is a challenging goal in and of itself!

As Heisig suggested , the kanji > keyword recall will take care of itself. Once you learn words and start reading textbooks etc. this "backward" recall will sort itself out. Sure you may have to look up the characters now and then, but once you do that this "kanji > keyword" link will come easily.

Here is a related discussion on the forum, including quotes from Heisig.

Now, if you REALLY want to test yourself "kanji to keyword"...

Solution 1 : Vocab Shuffle

The Vocab Shuffle modes are a better way to do this because at least you see the characters in context of actual Japanese words. And, you can learn new words.

If you do not use the SRS, and hence you have not added flashcards, use the "RTK Index" option.

If you use the SRS, then it's even better, you'll get a selection of words made of kanji you've successfully reviewed before.

While using Vocab Shuffle simply mouse over the kanji to see a tooltip with the keyword. You can test yourself like that before flipping the card. The kanji are also links to the study page!

Solution 2 : Kanji Review

You can always use the non-SRS reviews which used to be called "free reviews". In this mode you don't need to add flashcards. Enter a RTK range (eg. 20 to 50), or enter a RTK lesson.

Then simply check the "Kanji to Keyword (reverse mode)" checkbox!