How can I force dates/times to be in the past

[dyladan]

I'm sorry if this is an inappropriate place to ask this question but I didn't know where else to go.

I have an application that takes natural date and time queries and needs to assume that they happened in the past; rather than in the future, as duckling does. Right now this is my (very hacky) solution:

(p/parse :en$core exp [:time] context)
; if that result is in the future
(p/parse :en$core (str "last " exp) [:time] context)

This changes:

blah blah thursday blah

which returns the first thursday in the future, into:

blah blah last thursday blah

which returns Thursday in the past. Is there a better/supported way to do this?