Japanese - Polite form of 'dakke'?

-What would be the polite equivalent of 'dakke'? Would it be 'deshitakke'

>>> Yes I think you're right.

-or is that only used for past tense?

>>> No you can use it for both present and past. You can rephrase

「昔はよく小説を読んだもの*だっけ*」(past)

「みんなで遊んだのはこの路地*だっけ*」(past)

as

「昔はよく小説を読んだもの*でしたっけ*」

「みんなで遊んだのはこの路地*でしたっけ*」

AND

「君の年はいくつ*だっけ*」("How old are you?"/"How old did you say you are?"-- present)

as

「君の年はいくつ*でしたっけ*」

http://dictionary.goo.ne.jp/leaf/jn2/137261/m0u/

(We also have だったっけ, btw; この路地*だったっけ*, いくつ*だったっけ*)

-I have heard 'desukke' used at least once before, but I not sure whether this might be colloquial and not proper Japanese.

>>> Yeah だっけand でしたっけ are spoken language already but ですっけ sounds even more colloquial to me too. I kind of doubt it is considered proper Japanese but some people use it daily in casual conversation...