The offensive issue is soo multi faceted it will require a multi pronged attack.
For the DI, I think rosters are too small already. But you could tweak DI in other ways. Limit DI's on D, give them less offensive/defensive reps, only allow them to sub in if an imp goes down and is out for the game etc.
That said I think the meat of the problem is lack of creativity in offense. In the past 5 - 10 years the NFL and ncaa have stormed past the cfl in terms of developing offensive strategy. The roots of the systems we see flourishing today are old, but they were long relegated to desperate junk college programs with low talent and athleticism. Spread to run, RPO, QB option run, and Flex offenses that run tight stacks and spread with motion / post snap run football south of the border now. Mean while up here every one is doing the old 49ers offense as seen through the lense of paul lapolice. Mtl has tried to institute RPO under khari jones but has not been very good with it.
The CFL has lost touch with the ncaa as a venue for coaching talent. All we see now is former cfl players, who have cfl coaching lineages. No one breaks the mold. This applies to defense too. CFL coaching has become inbred past the point of The Hills Have Eyes. Each team should be carrying a none CFL coach like the global player we carry.
Back when Michael vick entered the NFL the majority of his runs were adlib. The designed run calls were extremely uninspired and not creative. If you watch what the ravens do now it's like a student who failed gr5 science compared to a physics doctoral candidate.
You could force defenses to have a certain amount of players on the line of scrimmage at the snap of the ball to make deep cover harder, or limit the men on the line to reduce qb pressure. You could greatly increase the penalty for punting out of bounds between the 20s, and change rules for alignment on blocking for punts so that it's much riskier and more worth while to go for it on 3rd down. More PI calls made the passing game much worse, but you could take out the ability to jam wrs. Lots of options exist to tweak the offensive rule set to enable offenses.
At the end of the day, CFL teams are doing a poor job of investing in and developing OL, especially imp ol. Teams aren't following the trends and making good use of the plethora of athletic qbs, and coaching is stagnant. The teams created this situation and now want every one else to suffer in order to fix it for them rather than doing the work and dealing with specific issues on their own.