Old thread, a new day,
Yes, I put a stem riser on my Burley soon after we started pedaling TWOGETHER (as Zonatandem would say) and have had no problems at all. Just check and double check that everything is always tight. You may need to do the cables again. This was an 8-speed flat bar which I converted to 9 speed, drop bar w/ R600 short reach brifters. For us, as a starter bike, it has worked out great.