Here's the skinny -
you can get your Seguro in Colombia through the Seguros del Estado S.A.
and pay for only the days you want to use it p costs about .50 USD a day
here's the offices in Cartagena to go to Carrera 8 no 34-62, Edeficio Banco de Bogota Piso 8, tel 664 7555, OR in Bogota to Calle 17 n0 10-16, Piso 3 tel3414646 OR in Medellin calle 53 no 45-45 oficina 1006 tel 2310799 OR in Popayan calle 4 no 8-26 tel 824 2922
.:: Seguros del Estado S.A. - Seguros de Vida del Estado S.A. ::.
not every office will sell by the day (or month or whatever) but if you call this (the one that does !)office they can explain to the office you are at how to do it : the oficina en Corridores in Bogota de seguros del estado tel 3414646 calle 17 no 10-16 piso 3

just insured a bike with fake papers, as well as my own no problem

I RECOMMEND DOING THIS NOW - last year in Colombia I was stopped about 10 times and never asked for insurance, this year so far 3 times by Trafico and asked each time ! I think the fine is about 200 usd and they take your bike and licenses right there...........I know people who go through without it....including me........but no more for me.
UPDATE .... JUST STOPPED TWICE MORE TODAY - same thing - looking for seguro - lots of motos being pulled over as well.....at all the checkpoints...

also - Chaleco is advised again - been hassled again in Bogota without it, you can get a cheapie for less tha 15 bucks USD with your placa numbers anywhere there are moto shops

Zigeuner