How to link to diff page using formatted search?

I've replaced the normal WebChanges with a table using formatted search, specifically $topic and $date.
I want to make the $date link to the most recent diff view but I am having trouble formulating this search.

My thinking is that I need to build a link identical to what's in Foswiki's footer, i.e. like this:
$topic?rev1=17;rev2=16

I know I can use $rev in the search format to get the current revision number, and I can use the Spreadsheet Plugin to subtract one. I would get something like:
%SEARCH{ . . . format="| $topic | [[ $topic?rev1=17;rev2=%CALC{"$rev-1"}% ][$date]]}%
(some spaces added for readability)

But in the above bold part, I'm drowning in the task of escaping all the nested % and $ characters in just the right way so they actually work.

Is there a smarter way to achieve this?