That would be problematic in infinite-attack mode - unless the drill rocket would freeze timer/disallow movement until explosion. (Like cake does)

Well, I have written a script which implements this feature. It is called “Game Hacks”, see here for more information:
http://hedgewars.org/node/6279

How to do it:
Load Game Hacks before starting the game and set the script parameter to one of the following:

• drillrockettimer=10s (timer is set to 10 seconds, replace “10” with your value of choice. Up to 3 decimal places are supported, so “4.123s” works, too)
• drillrockettimer=manual (player can use the timer keys to set the timer)

Important: When playing online, all players must have the script installed (also the same version, of course).

I agree with sheepluva that this would problematic in infinite attack mode. So it would be unwise to implement it.