There are 2 ways around this:
1/ Input a speed limit of 220/ 5000 on the vnav climb page speed restriction line. ( I've just picked 5000 as you probably won't be above 5000 until after porpa)
2/ Speed intervene on the MCP with 220kts once the aircraft is above acceleration altitude, closing the speed window once established on track outbound from porpa.
My understanding is that if you just open the speed window then the aircraft will fly at that speed but the aircraft will plan to fly the turn radius calculated as if the speed window is closed. Therefore if the aircraft had planned on going faster than 220 kts (for example 250 kts), then by just opening the speed window to 220 kts will cause the bank angle in the turn to reduce in order to fly the 250 kts track.
Therefore, the FMS needs to be programmed with a restriction and the most common way that I have seen is to program the VNAV CLB page on the FMS with a speed restriction of 220/5000'. Obviously you may have to change the height depending on aircraft performance.
Regards
csd