Yes Drop tanks can indeed be made stealthy, u just have to alter the paint, material and shape.
There is already one for f 35, f 22.
There was an AMCA slide show video where they showed Stealth drop tanks.
Stealth and aerodynamics don't go hand in hand; in most cases they act inversely with respect to each other. You may achieve stealth in frontal aspect but it may lead to increase in drag due to higher surface area.
Having said that, IMO there is no significant benefit in designing stealthier drop tanks which in most cases are ejected when fighters approach merge during dogfights.
For BVR part, due to limitation of FCS & missile range, the engagement range hovers around 100-120 kms. For Tejas, the tactic could be formulated which requires dropping of tanks while entering in this engagement range so that it could exploit its low RCS fully. In other words, BVR tactics dictate engaging target as near as possible to NEZ range of BVR AAMs, so Drop tank/No Drop tank it doesn't make any difference for Tejas if it stays out of the range of BVR missiles. You may detect it with AWACS but what can you do if you can't engage it with BVR AAM?
For strike missions, the loadout (Guided bombs/A-G Missiles) will spoil the party more as compared to Drop tanks. So again where is the benefit ?